• Adding value to milk by increasing its protein and CLA contents

      Murphy, J.J.; Stanton, Catherine; O'Donovan, Michael; Kavanagh, S.; Maher, J.; Patton, Joe; Mohammed, Riaz (Teagasc, 2008-08-01)
      The mid-summer milk protein study was undertaken on 34 commercial dairy farms in 2005 to evaluate the influence of dietary and management variables on milk protein content in mid-season. Data on grass composition, genetic merit of the herds and milk protein content were collected and analysed by multiple regression. Both calving date and genetic merit for milk protein content were significantly associated with milk protein content and were used as adjustment factors when evaluating the association between measures of grass quality and milk protein content. Milk protein content was associated with grass OMD (P = 0.04) and NDF content (P = 0.02) but not with CP content (P = 0.80). It is concluded that herds calving earlier, with a greater genetic merit for milk protein content and consuming better quality pasture would have greater milk protein contents in mid-season.
    • Adding value to milk by increasing its protein and CLA contents.

      Murphy, J.J.; Stanton, Catherine; O'Donovan, Michael; Kavanagh, S.; Maher, J.; Patton, J.; Mohammed, R. (Teagasc, 2008-08-01)
      Five experiments were undertaken in this project; one on mid-summer milk protein and four on milk CLA content. Thus the two main objectives of this project were to determine the factors associated with milk protein concentration in mid-summer and to investigate potential further strategies to increase the CLA content of pasture produced milk.
    • A comparison of energy balance and metabolic profiles of the New Zealand and North American strains of Holstein Friesian dairy cow

      Patton, Joe; Murphy, J.J.; O'Mara, Frank P.; Butler, Stephen T. (Cambridge University Press, 2008-06)
      The milk production, energy balance (EB), endocrine and metabolite profiles of 10 New Zealand Holstein Friesian (NZ) cows and 10 North American Holstein Friesian (NA) cows were compared. The NA cows had greater peak milk yields and total lactation milk yields (7387 v. 6208 kg; s.e.d.5359), lower milk fat and similar protein concentrations compared with the NZ cows. Body weight (BW) was greater for NA cows compared with NZ cows throughout lactation (596 v. 544 kg; s.e.d.515.5), while body condition score (BCS) tended to be lower. The NA strain tended to have greater dry matter intake (DMI) (17.2 v. 15.7 kg/day; s.e.d.50.78) for week 1 to 20 of lactation, though DMI as a proportion of metabolic BW was similar for both strains. No differences were observed between the strains in the timing and magnitude of the EB nadir, interval to neutral EB, or mean daily EB for week 1 to 20 of lactation. Plasma concentrations of glucose and insulin were greater for NA cows during the transition period (day 14 pre partum to day 28 post partum). Plasma IGF-I concentrations were similar for the strains at this time, but NZ cows had greater plasma IGF-I concentration from day 29 to day 100 of lactation, despite similar calculated EB. In conclusion, the results of this study do not support the premise that the NZ strain has a more favourable metabolic status during the transition period. The results, however, indicate that NZ cows begin to partition nutrients towards body reserves during mid-lactation, whereas NA cows continue to partition nutrients to milk production.
    • Effect of Feeding Mixed Forage Diets on Milk Production

      Fitzgerald, J.J.; Murphy, J.J. (Teagasc, 1999-02-01)
      For dairy farmers involved in winter milk production a high intake of forage is required by autumn calved dairy cows to produce a high milk yield with a moderate level of concentrate supplementation. Since intake of grass silage is often limiting, alternative forages or feeds may be needed to maximise forage intake. In areas not suitable for growing maize alternative forages need to be considered. These could include limited amounts of very high quality grass silage (DMD 750-800 g /kg), grazed autumn pasture or bulky by-product feeds, e.g. superpressed sugar beet pulp. An experiment was conducted involving 5 treatments in which a standard good quality grass silage (S) was partially replaced with either very high quality grass silage, which was either unwilted (U) or wilted (W), ensiled pressed sugar beet pulp (P) or with autumn pasture (G). These additional feeds were fed at a level of 5 kg DM/day to autumn calved cows in early lactation over a period of 8 weeks from late October to late December. The pressed pulp diet (P) included 0.5 kg DM soyabean meal to increase its protein level. The autumn grass was cut daily and fed indoors. The additional feeds were fed on top of the standard silage in individual feeding boxes and the standard silage was fed ad libitum to cows on all treatments. The cows were fed concentrates at 6 kg/day in two feeds on all treatments. The digestibility of the standard grass silage (754 g DMD/kg) was higher than planned and was only slightly less than that of the high quality supplementary silages (783 g DMD/kg). Feeding the U and W silages did not increase total forage intake but did increase milk yield by 1.7 - 1.9 kg/day compared with silage S alone. Milk fat and protein concentration tended to be reduced on the diets containing U and W silages, consequently yield of fat and protein were not significantly increased compared with silage S. Forage intake was increased by 8% (0.8 kg DM/day) when silage S was supplemented with autumn grass and milk yield was increased by 1.5 kg/day without affecting milk composition. Intake of silage was reduced by 37% by feeding grass. Feeding the pressed pulp supplement (P) increased intake of forage (+1.1 kg DM/day), increased milk yield by 2.7 kg/day and also improved milk protein concentration and yield (+121 g/day). Cows gained in liveweight to a similar extent on all diets. It was concluded that feeding pressed pulp with a good quality grass silage had the greatest effect on forage intake and milk production whereas feeding high quality grass silages or autumn grass had a smaller effect. Larger increases in intake and milk production would be expected from these feeds if the standard grass silage was of lower digestibility (~700 g DMD/kg), similar to average quality first cut silage.
    • The effects of altering milking frequency and/or diet in early lactation on the energy balance, production and reproduction of dairy cows.

      Murphy, J.J.; Mee, John F; McNamara, S.; Patton, J.; Kenny, David; Diskin, Michael; O'Mara, Frank P. (Teagasc, 2005-01-01)
      It has been suggested that negative energy balance (NEB) in the immediate post-partum period is potentially an important factor in the association between increasing milk output and declining reproductive performance. The objective of this project was to design an experimental model that could be used to impose different degrees of NEB immediately after calving and to examine the effect of this model on dry matter intake (DMI), milk production, energy balance (EB), metabolic and reproductive hormonal profiles, the onset and pattern of post-partum ovarian cyclicity and reproductive physiology around AI. Two experiments were carried out to evaluate the effects of milking frequency and diet on DMI, production, energy balance and blood metabolites and hormones in the first 4 weeks after calving and subsequent reproduction. Reducing milking frequency from either thrice or twice daily to once daily reduced DMI but also reduced milk production. This resulted in a better EB in once daily milked cows in both experiments, the reduction being significant in the first. Milk production during the 4-week treatment period was reduced by 23 and 20 percent by reducing milking frequency from thrice to once daily in experiments 1 and 2, respectively. There was a reduction of approximately 10 percent in the cumulative yield up to week 20 of lactation in experiment 1 and of approximately 9 percent in total lactation yield in experiment 2. Reducing milking frequency resulted in increased plasma glucose, insulin and IGF-1 concentrations and reduced non-esterified fatty acid (NEFA) and beta hydroxybutyrate (BHB) concentrations. Conception rates to first service or overall pregnancy rates were not different between milking frequency treatments but once daily milking resulted in a shorter interval to first ovulation than thrice daily milking, due to a higher proportion of cows on this treatment ovulating the first post-partum dominant follicle. Increasing the energy density 2 of the diet increased DMI and milk production with no consequent effect on energy balance. Logistic regression on the combined data from the two experiments showed that lower energy intake, greater NEB and lower milk protein content and were significantly associated with poorer conception to first service. Lower plasma IGF-1 concentrations in experiment 2 were also associated with a lower conception rate to first service. A third experiment which investigated protein concentration in the concentrate combined with concentrate feeding level post calving (for two groups of cows in different body condition score at calving) showed no effect of post calving diet on BCS change. Overall the results suggest that reducing milking frequency to once per day during the first 4 weeks of lactation reduces NEB and appears to be a suitable strategy for altering energy balance at this time. However, the short-term reduction in milking frequency immediately post partum reduces total lactation yields. Blood metabolite and hormonal concentrations indicate better energy balance for cows milked once daily. Increasing dietary energy density or reducing the protein content of the diet does not appear to be effective in changing energy balance in early lactation. Decreased NEB in the first 4 weeks post-partum is associated with an improved conception rate to first service.
    • Evaluation and Refinement of the French Protein System (PDI) under Irish Conditions

      Murphy, J.J.; Bohane, D.C.; Fitzgerald, J.J.; Kavanagh, S.; O'Mara, Frank P. (Teagasc, 2004-01-01)
      The CP and DM degradability of grazed grass (between April and October, inclusive) and grass silage samples (differing in cut number and treatment) was determined using the in situ technique and the results obtained were used to calculate the PDIE and PDIN values. The degradability data on 12 concentrate ingredients from a previous study (Woods, 2000) were used to estimate PDIE and PDIN values for these feedstuffs. The mean PDIE and PDIN values determined for grass were 81 g/kg and 127 g/kg DM, respectively and for grass silage were 60 g/kg and 94 g/kg DM. Regression analysis resulted in equations to predict the PDIN of samples of grazed grass (PDIN = 3.8 + 0.628 CP) (R²= 0.999) and grass silage (PDIN = 5.9 + 0.605 CP) (R²= 0.997), and the PDIE of grazed grass (PDIE = 181.4 - 0.104 NDF - 0.195 ash - 0.047 OMD) (R²= 0.987) and grass silage (PDIE = 27.7 + 0.083 DMD - 0.147 CP) (R²= 0.812). The PDIE and PDIN values of 11 of the 12 concentrate ingredients were similar to those used in the French Tables but the maize distillers’ grains in this study and those used in France would appear to be quite different products. The response to PDIE and PDIN in the diet of lactating cows was evaluated and the effect of better balancing the PDIE and PDIN supply on the efficiency of N utilisation was assessed. Twenty autumn calving cows were blocked in a complete Latin Square design and assigned to four different diets varying in PDIN and PDIE content. Each of the four treatments consisted of a concentrate, maize silage and grass silage in the proportions 37:38:25 on a DM basis. There were 4 periods of 4-week duration each. Diet A contained 92 g/kg DM of PDIE and 116 g/kg DM of PDIN. Diet B contained 103 g/kg DM of PDIE and 122 g/kg DM of PDIN. Diet C and D over supplied PDIN at 137 g/kg and 153 g/kg, respectively relative to PDIE at 111 g/kg DM. Dry matter intake increased significantly with the excess dietary PDIN relative to PDIE but there were no significant differences in milk yield and composition. Decreasing the supply of PDIE in the diet (i.e. diet A vs. B) resulted in no significant effect on milk or constituent yields but did significantly reduce the efficiency (kg milk / kg DMI) of milk production. There was also a significant reduction in the efficiency of milk produced per kg DMI with increasing dietary concentrations of PDIN and increasing PDIN: PDIE balance (B>C>D). Increasing the dietary PDIN from 122 to 153 g/kg DMI increased urine N (+54%), faecal N (+11%) and plasma urea concentrations (+75%). The results indicate that the optimum concentration of dietary PDI is approximately 103 g/kg DM for cows producing about 35 kg of milk per day. A better balance between PDIE and PDIN supply improves the efficiency of conversion of DM to milk and dietary protein.
    • Evaluation of fermented whole crop wheat, urea-treated processed whole crop wheat and maize silage for dairy cows

      Murphy, J.J.; Burke, F.; Kavanagh, S.; O'Donovan, Michael; Mulligan, F.J. (Teagasc, 2006-01-01)
      There has been increased interest in and increased usage of forages other than grass silage for feeding dairy cows during the winter period. This has arisen because of the inconsistency in making good quality grass silage and the low intake characteristics of this feed. The main objective of this project was to evaluate the effects on dairy cow intake and performance of offering fermented whole crop wheat (WCW) silage, urea-treated processed WCW and maize silage in mixtures with grass silage compared with grass silage alone. The value of these feeds as supplements to grazed grass in the Autumn for late lactation spring calving cows and their effect on dietary nitrogen (N) utilisation for milk protein production were also investigated. The first two experiments evaluated the effects of including 67% of the forage mixture on a dry matter (DM) basis as fermented WCW, urea-treated processed WCW (also known as “Alkalage”) or maize silage in comparison to grass silage alone in the diet of autumn calving cows. The fermented WCW and urea-treated processed WCW were harvested at a stubble height of approximately 20 cm. Sixty and 95% of the grain was milled/cracked in the urea-treated processed WCW in experiments 1 and 2, respectively. Forages were supplemented with concentrates of varying crude protein (CP) concentrations so as to maintain a similar CP concentration in the total dietary dry matter across treatments. In both experiments all the feeds were well preserved. The DM (g/kg) and starch contents (g/kg DM) in the fermented WCW, urea-treated processed WCW and maize silage in experiments 1 were 406 and 282, 733 and 324, 221 and 140 and in experiment 2 were 370 and 323, 763 and 341 and 302 and 324, respectively. Results from both experiments were similar. The three forage mixtures resulted in greater DM intake and greater fat plus protein production than grass silage. The largest effect on intake was obtained with the urea-treated processed WCW which probably reflected the greater DM content of this forage mixture compared with the others. Milk protein content was generally similar across the three forage mixtures and greater than on grass silage as the sole forage. In the third experiment short-straw urea-treated processed WCW (harvested at a stubble height of 35 cm) was evaluated in comparison to the fermented WCW (harvested at a stubble height of 20 cm), maize silage and grass silage. The DM (g/kg) and starch (g/kg DM) contents in the fermented WCW, urea-treated processed WCW and maize silage were 389 and 316, 795 and 382 and 346 and 301, respectively. Fifty nine percent of the grain was cracked/processed in the urea-treated processed UP-WCW .Level of inclusion of forages in the diets was the same as in the first two experiments and total dietary CP was again maintained at a similar concentration across treatments by offering concentrates of varying CP concentrations. The higher harvesting height of the urea-treated processed WCW resulted in a greater starch concentration in this feed in comparison to the first two experiments. The results however were very similar to those obtained in the first two experiments with the forage mixtures again increasing DM intake and fat plus protein yield. Inclusion of the short-straw urea-treated processed WCW did not result in greater fat plus protein production compared with the inclusion of fermented WCW or maize silage. The greatest efficiency of conversion of dietary nitrogen (N) to milk N was achieved with the maize silage mixture and the least efficiency with the urea-treated process WCW mixture. In experiment 4 the nutritive value of fermented WCW, urea-treated processed WCW and maize silage were evaluated in comparison to a concentrate as supplements to grazed grass for spring calving cows in the autumn. A treatment with a high grass allowance of 24 kgDM (> 4 cm)/cow per day was also included while the grass allowance on the supplemented treatments was restricted to 17 kgDM (> 4 cm)/cow per day. All the supplemented treatments and the high grass allowance treatment gave greater milk yields than the unsupplemented restricted grass treatment. The concentrate supplement resulted in the greatest solids corrected milk yield and this was greater than any of the forage supplemented treatments which were not significantly different from one another. In the final experiment the output of N in milk, urine and faeces was measured when grass silage, fermented WCW, urea-treated processed WCW and maize silage were fed as the sole forages plus 6 kg of a concentrate containing 338 g crude protein/kg DM. The proportion of consumed N excreted in urine and faeces was greatest on grass silage and urea-treated processed WCW with fermented WCW and maize silage resulting in the greatest proportion of consumed N being excreted in milk. Overall, the project demonstrated that including either type of WCW or maize silage with grass silage increased fat plus protein production and protein concentration to a similar extent compared to grass silage as the sole forage. All three forages increased DM intake with the greatest increase observed with urea-treated processed WCW. Because of this greater intake resulting in similar fat plus protein production conversion of dietary DM to milk solids was less efficient on urea-treated processed WCW based diets than on fermented WCW or maize silage based diets. Grass silage and urea-treated processed WCW based diets were least N efficient with less dietary N being incorporated into milk N than on fermented WCW or maize silage based diets. Comparing the responses on the forage mixtures relative to one another and to grass silage across experiments 1 to 3 indicates that neither degree of grain processing or harvesting height (within the ranges studied here) are of substantial importance in determining the nutritive value of urea-treated processed WCW. All of the three alternative forages gave similar solids corrected milk yield responses when used as buffer feeds for spring calved cows at pasture in the autumn but these responses were less than 50% of the response to a concentrate supplement.
    • Extended lactations in a seasonal-calving pastoral system of production to modulate the effects of reproductive failure

      Butler, Stephen T.; Shalloo, Laurence; Murphy, J.J. (American Dairy Science Association and Elsevier Inc., 2010-03)
      This study was conducted to determine whether extending the calving interval (CI) to 24 mo would be an alternative to culling and replacing cows that had failed to become pregnant. Forty six non-pregnant lactating cows were assembled in Nov 2004 and assigned to receive either 3 kg (low) or 6 kg (high) of concentrate supplement and a basal diet of grass silage and maize silage over the winter period (13 wk). Cows returned to pasture in late March, and received 1 kg concentrate/d until dry-off (milk yield <5 kg/d). Cumulative milk production was calculated from calving to the end of Nov 2004 (12 mo CI), and from the start of Dec 2004 until dry off in 2005 (extended lactation part of 24 mo CI). High winter feeding resulted in greater milk production over the winter confinement (20.0 ± 0.3 vs. 17.8 ± 0.3 kg/d), and had a carryover effect during the remainder of the 24 mo CI period (5,177 vs. 4,686 kg; SEM = 173 kg). At the end of the study, cows were ranked on cumulative milk solids, and separated into 3 groups (R1, R2, and R3). During the 24 mo CI, milk yields were 7,287, 6,267 and 5,273 kg (SEM = 308 kg) in Year 1, and 5,738, 4,836, and 4,266 (SEM = 241 kg) in Year 2 for R1, R2, and R3, respectively. Eighty five percent of the cows became pregnant during the breeding season of yr 2, with a conception rate to first service of 52%. An economic analysis of different Ranks with a 12 mo CI, a 24 mo CI, and an annualized herd effect, which compared an efficient spring calving system with a system that had 30% recycled cows in R1 and 10% recycled cows in R3 was carried out. Farm profit was reduced by 60% and 65% at a milk price of 22.3 c/L with the corresponding values of 17% and 30% for a milk price of 30 c/L, respectively, when R1 and R3 systems were compared with an efficient spring milk (12 mo CI) production system. Within a spring system where 30% and 10% of R1 and R3 animals are subjected to extended lactations, the profit difference was substantially reduced compared to an efficient spring system, The results indicated that lactations with a 24 mo CI may be a viable alternative to culling non-pregnant cows, and economically more suited to higher producing cows.
    • Genetic Variants of Milk Proteins - Relevance to Milk Composition and Cheese Production.

      Fitzgerald, R.J.; Walsh, D.; Guinee, Timothy P.; Murphy, J.J.; Mehra, Raj; Harrington, D.; Connolly, J.F. (Teagasc, 1999-07-01)
      Objectives: (i) to develop rapid screening procedures for the determination of milk protein polymorphism (genetic variants) (ii) to determine the frequency distribution of milk protein genetic variants in a large population of Irish Holstein-Friesians and to determine if there was an association between κ-casein variant and milk yield and composition in this group of animals, and (iii) to make Cheddar and low-moisture part-skim Mozzarella cheese from different κ-casein genetic variant milks and to assess any effect on cheese yield, composition and functional characteristics. Conclusions:Analysis of 6,007 individual Irish Holstein-Friesian milks showed that the phenotype distribution of the κ-casein BB variant was very low at 1.98% compared to 53.07% for κ-casein AA and 44.95% for κ-casein AB. While no statistically significant associations were observed between κ-casein variant and milk yield and composition, κ-casein BB variant milks had superior rennet coagulation properties to that of the AA or AB variants. Generally, κ-casein variant had little effect on compositional attributes of cheese apart from FDM (fat in dry matter) which was significantly higher in cheeses from κ-casein BB milk than in those from κ-casein AA milk. Generally, κ-casein variant had no significant effects on either primary or secondary proteolysis, or on the sensory and/or textural characteristics of Cheddar or Mozzarella cheese throughout ripening; or on the functional characteristics (e.g. flow and stretch) of baked Mozzarella on storage for 90 days at 4°C. However, κ-casein BB variant milk gave significantly higher actual, and moisture adjusted yields of Cheddar and Mozzarella cheese than either κ-casein AB or AA variant milks. For example, the moisture adjusted Cheddar yield from κ-casein BB milk was 8.2% higher than from κ-casein AA milk. In the case of Mozzarella, the moisture adjusted yield was 12% higher. Based on the results, it is estimated that the actual yield of cheese in a plant producing 20,000 tonnes per year from κ-casein AA milk would increase to approximately 21,180 tonnes of Cheddar, or 21,780 tonnes of Mozzarella if made from κ-casein BB milk. Where κ-casein AB milk is used instead of κ-casein BB milk, the estimated yield of Mozzarella would increase to 21,580 tonnes.
    • The Importance of Different On-Farm Feeding and Management Practices on Milk Protein Concentration and Yield

      Murphy, J.J.; Harrington, D.; Cliffe, D.; Crilly, J. (Teagasc, 2006-01-01)
      The objective of this project was to identify the most important factors which influence milk protein concentrations and yields on farms. Data collected on approximately 300 DairyMis farms were subjected to statistical evaluation by regression analysis, analysis of variance and factor analysis. The range in protein concentrations was 12% of the mean value compared to a variation in protein yield of 86% of the mean. The range in milk yield was 90% of the mean value. Initially data from 1995 were analysed. The regression model used only accounted for 4% of the variation between farms in milk protein concentration but for over 97% of the variation in milk protein yield. Milk protein yield was highly correlated with milk yield. Confining the analysis to Spring-calving herds only in 1995 (n=128) gave similar results but including genetic data in the regression model, for those spring-calving herds for which it was available (n = 36), explained approximately 25% of the variation in protein concentration. Analysis of variance on the spring-calving herd data (for 1994, 1995 and 1996) divided into quartiles on the basis of protein concentration indicated that higher protein concentration was associated with later calving, a higher proportion of milk produced on pasture and lower milk yield per cow. Factor analysis on all herds in 1994, 1995 and 1996 indicated that higher protein concentration was associated with Spring-calving herds, larger herds and with grass based milk production. These three factors accounted for 8% of the observed variation in milk protein concentration.
    • Maize silage for milk production - Part 1: Effect of the quality of maize silage on milk

      Fitzgerald, J.J.; Murphy, J.J.; O'Mara, Frank P.; Culleton, Noel (Teagasc, 1998-11-01)
      Ensiled forage maize is an alternative or complementary forage to grass silage and is the main source of forage for ruminant livestock in many European countries. The growing of maize for silage was tried unsuccessfully in Ireland in the 1970’s, was resumed in the late 1980’s and is now well established in suitable areas in the south and east of Ireland. However, variation in growing conditions and summer radiation can result in considerable variation in the yield, maturity and feeding value of the crop from year to year and between regions or locations within years. A series of experiments were conducted at Moorepark and at Johnstown Castle Research Centre to evaluate the role of maize silage in the diet of lactating dairy cows, the effect of variation in the quality (starch content and digestibility) of maize silage, the proportion of maize silage in the forage and the effect of harvesting date of immature maize silage on feed intake, milk production and milk composition compared with an all grass silage based diet. Grass silages of moderate or high digestibility were used. These studies were carried out with cows in early or mid lactation or at both stages of lactation. The forages were supplemented with concentrates at low to moderate levels of feeding (4-7 kg/cow/day). The concentrates generally contained a high level of crude protein (220- 250 g CP/kg fresh weight) to balance the low level of crude protein in maize silage. The experiments were conducted over periods of 7-9 weeks.
    • Maize silage for milk production - Part 2: Effect of concentrate quality and quantity fed withmaize silage based forages on milk production

      Fitzgerald, J.J.; Murphy, J.J.; Culleton, N. (Teagasc, 1998-11-01)
      In some of the studies outlined in Part 1 of this report, mixed forages containing grass silage and a high proportion (60%) of maize silages varying in maturity and starch content were supplemented with concentrates at different levels to compare the response in milk production with a maize silage based forage and with good quality grass silage as the sole forage. The most suitable type of energy ingredient in the concentrate, i.e. high starch or low starch, high fibre ingredients, as supplements to maize silage based forages or grass silage was investigated. A range of levels of crude protein in the concentrate were examined in one study to determine the optimum level of crude protein in the supplement for maize silage based forages compared with grass silage.
    • Responses of North American and New Zealand strains of Holstein–Friesian dairy cattle to homeostatic challenges during early and mid-lactation

      Patton, Joe; Murphy, J.J.; O'Mara, Frank P.; Butler, Stephen T. (Cambridge University Press, 2009-02)
      This study investigated the physiological basis of differences in nutrient partitioning between the North American (NA) and New Zealand (NZ) strains of Holstein Friesian cattle by determining the responses to homeostatic challenges at two stages of lactation. Glucose tolerance tests, epinephrine challenges, and insulin challenges were carried out on consecutive days commencing on day 32 ± 0.48 (mean ± s.e.m) of lactation (T1) and again commencing on day 137 ± 2.44 of lactation (T2). The insulin and non-esterified fatty acid (NEFA) responses to glucose infusion did not differ between the strains. The NZ strain had a greater clearance rate (CR) of glucose (2.04 vs. 1.66 % / min) and tended to have a shorter (34.4 vs. 41.1 min) glucose half-life (t½) at T2 when infused with glucose. The NA cows had a greater glucose response to epinephrine infusion across T1 and T2, and tended to have a greater insulin response to epinephrine infusion. Plasma NEFA concentration declined to similar nadir concentrations for both strains at T1 in response to insulin, though from a higher basal concentration in NA cows, resulting in a greater (-2.29 vs. -1.38) NEFA area under the response curve (AUC) for NA cows. Glucose response to insulin varied with time, tending to be greater for NA at T1, but tending to be lower for NA at T2. The results indicated that NA cows had a greater glycogenolytic response to epinephrine, but both strains had similar lipolytic responses. The results also imply that higher basal circulating NEFA concentrations in the NA strain in early lactation were not due to diminished adipose tissue responsiveness to insulin. There were indications that glucose clearance rate was greater in NZ cows in mid-lactation, and may form the basis of increased body tissue accretion during mid- to late-lactation in this strain.
    • Short Communication: The effect of dry period duration and dietary energy density on the rennet gelation properties of milk in early lactation

      Butler, Stephen T.; de Feu, M.A.; O'Brien, Bernadette; Guinee, Timothy P.; Murphy, J.J. (American Dairy Science Association and Elsevier Inc., 2010-02)
      This study was carried out to examine the effects of decreasing dry period duration (DP) and altering the energy density of the diet during early lactation on the rheological characteristics of milk. Forty mature Holstein-Friesian cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to one of two dry period treatments and one of two nutritional treatments. The dry period treatments were continuous milking (CM) or an 8-week standard dry period (SDP), and the nutritional treatments were a standard energy diet (SE) or a high energy diet (HE). Actual dry period lengths were 6.3 ± 1.7 days and 62.1 ± 1.9 days for cows for the CM and SDP treatments, respectively. Milk samples were collected at 2, 6 and 10 weeks postpartum. The concentration of fat, protein and lactose was determined in each sample. The rennet gelation properties were measured at 31 ° C using dynamic low-amplitude strain oscillatory rheometry. The following parameters were obtained from the resultant elastic shear modulus (G′): gelation time (GT), maximum curd firming rate (CFRmax) and gel strength (GS). Reducing dry period duration from 62 to 6 days resulted in increases in milk protein concentration (31.8 vs. 34.7 g/kg; P < 0.001), CFRmax (2.58 vs. 3.60 Pa/min; P < 0.001) and GS (69.4 vs. 90.5 Pa; P = 0.003). Raising the dietary energy density decreased percentage milk fat (43.1 vs. 37.7 g/kg; P < 0.001) but otherwise had no effect. GS was correlated with CFRmax (r = 0.98; P < 0.001), and both variables were correlated with milk protein concentration (r = 0.71; P < 0.001, and r = 0.73; P < 0.001, respectively). The results indicate that decreasing the duration of DP increased milk protein concentration and improved the rennet gelation properties of milk, but that dietary energy density had little effect.