• Insemination factors affecting the conception rate in seasonal calving Holstein-Friesian cows

      Buckley, Frank; Mee, John F; O'Sullivan, Kathleen; Evans, R. D.; Berry, Donagh; Dillon, Pat; AIB Bank; Holstein UK and Ireland; National AI Co-ops; Dairy Levy Research Trust (EDP Sciences, 2003-11)
      Differences in conception rate to first service between artificial inseminations (AI) carried out by commercial AI operators (CAI) or do-it-yourself operators (DIY), between natural service (NAT) and AI, between different AI sires, and between fresh and frozen-thawed semen, on Irish commercial dairy farms, were studied using logistic regression. The study comprised 12 933 potential first inseminations from 77 spring-calving dairy herds. The data were recorded during 1999 and 2000. Amongst the total, 4 394 cows had repeated records across the two years. Adjustment variables included: herd, year, parity, calving period, calving to service interval, herd size, proportion of North American Holstein-Friesian genes, peak milk yield, semen fresh or frozen-thawed status, AI sire and a cow history variable to account for the correlation structure that may exist between performance records of cows present in both years of the study. Interactions of interest were tested but were non-significant. No significant association was observed between the category of AI operator and the likelihood of conception rate to first service (PREG1). The variation in PREG1 observed within the category of operator (CAI and DIY) was investigated using the Levene test for homogeneity of variance. There was no difference between the level of variation observed within CAI and DIY operators. There were significant differences in the likelihood of PREG1 between different AI sires. Amongst the 40 most commonly used AI sires, 3 sires had a lower likelihood of PREG1 (P < 0.05) when compared to the reference AI sire (sire with PREG1 similar to the mean of the group). There was a tendency for a reduced likelihood of PREG1 with the use of fresh semen compared to frozen-thawed semen ( , P = 0.067). Amongst the adjustment variables in the model, those significantly associated with the likelihood of PREG1 included the herd, calving period, calving to first service interval and peak milk yield. No significant difference in the likelihood of PREG1 was observed between AI and NAT.
    • Relationships Among Milk Yield, Body Condition, Cow Weight, and Reproduction in Spring-Calved Holstein-Friesians

      Buckley, Frank; O'Sullivan, K.; Mee, John F; Evans, R.D.; Dillon, Pat; Allied Irish Bank; Holstein UK and Ireland; National AI Co-Ops; Irish Dairy Devy (Elsevier, 2003-07)
      Relationships among milk production, body condition score (BCS), body weight (BW), and reproduction were studied using logistic regression on data from 6433 spring-calving Holstein-Friesian dairy cows in 74 commercial herds. Multivariate models were adjusted for herd, breeding value for milk yield, proportion of Holstein-Friesian genes, lactation number, calving period, and degree of calving assistance. Significant associations between reproductive measures and components of energy balance were identified. Higher 200-d milk protein content and higher protein-to-fat ratio at start of breeding were associated with increased likelihood of submission for breeding in the first 21 d of the breeding season (SR21). High 100-d cumulative milk yield as a proportion of estimated 305-d milk yield (low persistency) was associated with a lower likelihood of pregnancy to first service (PREG1), whereas cows reaching peak milk yields earlier tended to have higher PREG1. Cows that reached nadir milk protein content relatively late in lactation had lower PREG1. Milk yield at first service and 305-d milk protein content were positively associated with the likelihood of pregnancy after 42 d of breeding (PR42). Higher 305-d milk lactose content was associated with increased PREG1 and PR42. Mean BCS at 60 to 100 d of lactation was positively associated with both SR21 and PR42, whereas nadir BCS was positively associated with PREG1. Cows with precalving BCS > 3.0 that also lost > 0.5 BCS unit by first service had lower PR42. More BW gain for 90 d after start of breeding was associated with higher SR21 and PREG1; more BW gain for 90 d after first service was associated with higher PR42. Milk protein and lactose content, BCS, and BW changes are important tools to identify cows at risk of poor reproduction.