Genetic (co)variances between body condition score (BCS), body weight (BW), milk production, and fertility-related traits were estimated. The data analyzed included 8591 multiparous Holstein-Friesian cows with records for BCS, BW, milk production, and/or fertility from 78 seasonal calving grass-based farms throughout southern Ireland. Of the cows included in the analysis, 4402 had repeated records across the 2 yr of the study. Genetic correlations between level of BCS at different stages of lactation and total lactation milk production were negative (-0.51 to -0.14). Genetic correlations between BW at different stages of lactation and total lactation milk production were all close to zero but became positive (0.01 to 0.39) after adjusting BW for differences in BCS. Body condition score at different stages of lactation correlated favorably with improved fertility; genetic correlations between BCS and pregnant 63 d after the start of breeding season ranged from 0.29 to 0.42. Both BW at different stages of lactation and milk production tended to exhibit negative genetic correlations with pregnant to first service and pregnant 63 d after the start of the breeding season and positive genetic correlations with number of services and the interval from first service to conception. Selection indexes investigated illustrate the possibility of continued selection for increased milk production without any deleterious effects on fertility or average BCS, albeit, genetic merit for milk production would increase at a slower rate.

Interactions between genotype and environment are becoming increasingly important as cattle genotypes are being managed in a diverse range of environments worldwide. The objective of this study was to investigate if there is an interaction of strain of Holstein-Friesian cows (HF) by grass-based feed system that affects milk production, body weight, and body condition score. Three strains of HF were compared on 3 pasture-based feed systems over 3 consecutive years. The 3 strains of HF were: high production North American, high durability North American, and New Zealand. The 3 grass-based feeding systems (FS) were: a high grass allowance system (MPFS), a high concentrate system (HCFS), and a high stocking rate system (HSFS). There was a separate farmlet for each FS and a total of 99, 117, and 117 animals were used in yr 1, 2, and 3 respectively, divided equally between strains of HF and FS. The high production cows produced the highest yield of milk, the New Zealand the lowest, and the high durability animals were intermediate. Milk fat and protein content were higher for the New Zealand strain than for the high production and high durability strains. The New Zealand strain had the lowest body weight and the highest condition score, whereas the high durability strain had the highest body weight, and the high production strain had the lowest condition score. There was a strain x FS interaction for yield of milk, fat, and protein. The milk production response to increased concentrate supplementation (MPFS vs. HCFS) was greater with both the high production and high durability strains (1.10 kg of milk/kg of concentrate for high production; 1.00 kg of milk/kg of concentrate for high durability) than the New Zealand strain (0.55 kg of milk/kg of concentrate). The results indicate that the optimum strain of HF will vary with feed system.

A stochastic budgetary simulation model of a dairy farm was developed to allow investigation of the effects of varying biological, technical, and physical processes on farm profitability. The model integrates animal inventory and valuation, milk supply, feed requirement, land and labor utilization, and economic analysis. A key model output is the estimated distribution of farm profitability, which is a function of total receipts from milk, calves, and cull cows less all variable and fixed costs (including an imputed cost for labor). An application of the model was demonstrated by modeling 2 calving patterns: a mean calving date of February 24 (S1) and a mean calving date of January 27 (S2). Monte Carlo simulation was used to determine the influence of variation in milk price, concentrate cost, and silage quality on farm profitability under each scenario. Model validation was conducted by comparing the results from the model against data collected from 21 commercial dairy farms. The net farm profit with S1 was 53,547 euros, and that with S2 was 51,687 euros; the annual EU milk quota was 468,000 kg, and farm size was 40 ha. Monte Carlo simulation showed that the S1 scenario was stochastically dominant over the S2 scenario. Sensitivity analyses showed that farm profit was most sensitive to changes in milk price. The partial coefficients of determination were 99.2, 0.7, and 0.1% for milk price, concentrate cost, and silage quality, respectively, in S1; the corresponding values in S2 were 97.6, 2.3, and 0.1%. Validations of the model showed that it could be used with confidence to study systems of milk production under Irish conditions.

The objective of this study was to determine the effect of inbreeding on milk production, somatic cell count, fertility, survival, calving performance, and cow conformation in Irish Holstein-Friesian pluriparous dairy cows. Inbreeding was included in a linear mixed model as either a class variable or a continuous variable, where higher order polynomials of the latter were also tested in the model as an indicator of nonlinear inbreeding depression. The effects of dam inbreeding and calf inbreeding on calving-related traits were analyzed separately. Inbreeding had a deleterious effect on most of the traits analyzed, although inbreeding depression was sometimes nonlinear or differed significantly across parities. A primiparous animal, 12.5% inbred (i.e., following the mating of noninbred half-sibs), had milk, fat, and protein yields reduced by 61.8, 5.3, and 1.2 kg, respectively; fat and protein concentrations reduced by 0.05 and 0.01%, respectively; and somatic cell scores (i.e., natural log of somatic cell count divided by 1,000) increased by 0.03. The 12.5% inbred animal was also expected to have a 2% greater incidence of dystocia, a 1% greater incidence of stillbirth, a 0.7% greater incidence of male calves, an increase in calving interval of 8.8 d, an increase in age at first calving of 2.5 d, and a reduced survival to second lactation of 4 percentage units. Inbred animals were also taller, narrower, and more angular. Although the effects of inbreeding were statistically significant, they were small and are unlikely to cause great financial loss on Irish dairy farms.

Genetic (co)variances between body condition score (BCS), body weight (BW), milk yield, and fertility were estimated using a random regression animal model extended to multivariate analysis. The data analyzed included 81,313 BCS observations, 91,937 BW observations, and 100,458 milk test-day yields from 8725 multiparous Holstein-Friesian cows. A cubic random regression was sufficient to model the changing genetic variances for BCS, BW, and milk across different days in milk. The genetic correlations between BCS and fertility changed little over the lactation; genetic correlations between BCS and interval to first service and between BCS and pregnancy rate to first service varied from -0.47 to -0.31, and from 0.15 to 0.38, respectively. This suggests that maximum genetic gain in fertility from indirect selection on BCS should be based on measurements taken in midlactation when the genetic variance for BCS is largest. Selection for increased BW resulted in shorter intervals to first service, but more services and poorer pregnancy rates; genetic correlations between BW and pregnancy rate to first service varied from -0.52 to -0.45. Genetic selection for higher lactation milk yield alone through selection on increased milk yield in early lactation is likely to have a more deleterious effect on genetic merit for fertility than selection on higher milk yield in late lactation.