Browsing Animal & Grassland Research & Innovation Programme by Funder "Dairy Levy Research Trust Ireland"
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Effect of grass dry matter intake and fat supplementation on progesterone metabolism in lactating dairy cowsProgesterone (P4) metabolism in dairy cattle can be manipulated by alterations in dry matter intake and diet composition. Our objectives were to determine the effects of grazing allowance and fat supplementation on P4 metabolism in lactating dairy cows. Forty mid- to late-lactation Holstein-Friesian dairy cows were used in a completely randomized block design, with a 2 × 2 factorial arrangement of treatments. Cows were assigned to receive 1 of 2 pasture allowances (ad libitum allowance [AL], 9.5 kg dry matter per day, or restricted allowance [R] 7 kg dry matter per day) and 1 of 2 fat supplementation treatments (750 g per day saturated fat [F] or no fat supplement [NF]). All cows received an additional 4 kg per day of concentrate. Grass dry matter intake (GDMI) was measured 5 wk after the initiation of dietary treatment. Cows were treated with prostaglandin F2α (PGF2α) to eliminate the endogenous source of P4, and two intravaginal progesterone-releasing devices (CIDR) were inserted into each cow for a period of 8 days. Regular blood samples were taken before and after the removal of the intravaginal progesterone-releasing devices, and analyzed for P4 concentrations. The half-life (t½) and metabolic clearance rate (MCR) of P4 was calculated for each cow. There was no effect of GDMI or fat supplementation on the t½ or MCR of P4. There was a tendency for an interaction between GDMI and fat supplementation on the t½ of P4; cows on the restricted-F diet tended to have a longer P4 t½ than cows on the ad libitum-F diet. It was concluded that greater alterations in GDMI than achieved in the current study are required to change P4 metabolism. A combination of fat supplementation and restricted feeding slows P4 clearance, which may have beneficial implications for fertility.
Effect of supplementation with different fat sources on the mechanisms involved in reproductive performance in lactating dairy cattleSupplementary fat positively influences reproductive performance in dairy cattle, although the mechanisms involved are not clearly defined. Our objective was to determine the effects of four different fat supplements on follicle development, plasma steroid hormone concentrations and prostaglandin (PG) synthesis in lactating dairy cattle. Forty-eight early lactation Holstein-Friesian cows (21 primiparous, 27 multiparous) were used in a completely randomized block design. Cows were fed the same basal TMR diet and received one of four fat supplements: (i) palmitic acid (18:0 fatty acid; Control), (ii) flaxseed (rich in 18:3 n-3 fatty acid; Flax), (iii) conjugated linoleic acid (a mixture of cis-9, trans-11 and trans-10, cis-12 isomers; CLA), and (iv) fish oil (rich in 20:5 and 22:6 n-3 fatty acids; FO). All lipid supplements were formulated to be isolipidic; palmitic acid was added as necessary to provide a total lipid supplement intake of 500 g/day. Cows were synchronized to be in estrus on Day 15 of dietary treatment. All antral follicles were counted, and dominant follicles, subordinate follicles and corpora lutea were measured daily via transrectal ovarian ultrasonography for one complete estrous cycle. Blood samples were collected daily, and selected samples were analyzed for progesterone, estradiol, insulin-like growth factor-1, insulin, cholesterol and non-esterified fatty acids. Estrus was synchronized a second time, and liver and endometrial biopsies were collected on Day 7 of the estrous cycle. Gene expression was evaluated for a number of genes involved in prostaglandin synthesis (endometrium) and fatty acid uptake and utilization (liver). Fat supplementation had little effect on follicle development. Cows receiving supplementary n-3 fatty acids had lesser plasma progesterone (P4) and smaller corpora lutea than cows receiving the CLA or Control supplements. Effects of fat supplementation on the endometrial expression of genes involved in PG synthesis were minor. Hepatic expression of SREBF1, ASCL1 and FABP1 was reduced by FO supplementation. Reduced plasma P4 in n-3 supplemented cows may lead to a suboptimal uterine environment for embryo development and hence reduced fertility compared to cows receiving the control or CLA supplements.
Evaluation of protocols to synchronize estrus and ovulation in seasonal calving pasture-based dairy production systemsLactating dairy cows (n = 1,538) were enrolled in a randomized complete block design study to evaluate protocols to synchronize estrus and ovulation. Within each herd (n = 8), cows were divided into 3 calving groups: early, mid, and late, based on days in milk (DIM) at mating start date (MSD). Early calving cows (n = 1,244) were ≥42 DIM at MSD, mid-calving cows (n = 179) were 21 to 41 DIM at MSD, and late-calving cows (n = 115) were 0 to 20 DIM at MSD. Cows in the early, mid-, and late-calving groups were synchronized to facilitate estrus or timed AI (TAI) at MSD (planned breeding 1; PB1), 21 d (PB2), and 42 d (PB3) after MSD, respectively. For each PB, cows in the relevant calving group were stratified by parity and calving date and randomly assigned to 1 of 4 experimental groups: (1) d −10 GnRH (10 μg of i.m. buserelin) and controlled internal drug release insert (CIDR; 1.38 g of progesterone); d −3 PGF2α (25 mg of i.m. dinoprost); and d −2 CIDR out and AI at observed estrus (CIDR_OBS); (2) same as CIDR_OBS, but GnRH 36 h after CIDR out and TAI 18 h later (CIDR_TAI); (3) same as CIDR_TAI, but no CIDR (Ovsynch); or (4) untreated controls (CTRL). The CIDR_OBS, CIDR_TAI, and Ovsynch had shorter mean intervals from calving to first service compared with the CTRL (69.2, 63.4, and 63.7 vs. 73.7 d, respectively). Both CIDR_OBS (predicted probability; PP of pregnancy = 0.59) and CIDR_TAI (PP of pregnancy = 0.54) had increased odds of conceiving at first service compared with Ovsynch [PP of pregnancy = 0.45; odds ratio (OR) = 1.81 and OR = 1.46, respectively], and Ovsynch had decreased likelihood of conceiving at first service (OR = 0.70) compared with CTRL (PP of pregnancy = 0.53). Both CIDR_TAI hazard ratio; HR [95% confidence interval = 1.21 (1.04, 1.41)] and Ovsynch [HR (95% confidence interval) = 1.23 (1.05, 1.44)] were associated with an increased likelihood of earlier conception compared with the CTRL. A greater proportion of cows on the CIDR_TAI treatment successfully established pregnancy in the first 42 d of the breeding season compared with the CTRL (0.75 vs. 0.67 PP of 42-d pregnancy, respectively). Protocols to synchronize estrus and ovulation were effective at achieving earlier first service and conception in pasture-based seasonal calving dairy herds. However, animals that conceived following insemination at observed estrus had a decreased likelihood of embryo loss to first service compared with animals bred with TAI (PP of embryo loss after first service = 0.05 vs. 0.09; OR = 0.52).
Genetic merit for fertility traits in Holstein cows: III. Hepatic expression of somatotropic axis genes during pregnancy and lactationThe objective of this study was to characterize the circulating concentrations of insulin-like growth factor-I (IGF-I) and the hepatic expression of key genes regulating the somatotropic axis in cows divergent in genetic merit for fertility traits but with similar genetic merit for milk production traits. A total of 11 cows with good genetic merit for fertility (Fert+) and 12 cows with poor genetic merit for fertility (Fert−) underwent liver biopsy by percutaneous punch technique on d 20 (± 6.7 d) prepartum and on d 2 (± 1.5 d), d 58 (± 3.7 d), d 145 (± 13 d), and d 245 (± 17.1 d) postpartum. Total RNA was isolated and the mRNA expression of growth hormone receptor (GHR 1A and GHRtot), IGF-I, janus tyrosine kinase 2 (JAK2), signal transducer and activator of transcription 5B (STAT5B), suppressor of cytokine signaling 3 (SOCS-3), acid-labile subunit (ALS), and IGF-binding proteins (IGFBP1 to IGFBP6) were measured by real-time quantitative PCR. During lactation, the circulating concentrations of IGF-I were 34% greater in Fert+ cows. The Fert+ cows had increased mean expression of IGF-I mRNA during the study; however, the difference in IGF-I mRNA abundance between Fert+ and Fert− cows was most pronounced at d 145 and 245. The expression of IGFBP3 and ALS transcript was similar in Fert+ and Fert− cows for the duration of the study. The Fert− cows, however, had greater expression of IGFBP2, IGFBP4, IGFBP5, and IGFBP6. Genotype had no effect on mRNA abundance of GHR 1A, STAT5B, JAK2, or SOCS-3. Genetic merit for fertility traits affects hepatic expression of key genes of the somatotropic axis regulating the synthesis, bioavailability, and stability of circulating IGF-I.