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Relationships between birth season versus early life starter intake and growth and first lactation performance of Holstein dairy cows
The objective was to determine the effect of birth season on early life starter intake, growth, and on first lactation performance of Holstein cows. Data was collected from birth yr of 2004 to 2012 for 2,880 Holstein cattle. Calves were received from 3 commercial dairy farms and enrolled in 37 different calf research trials at SROC from 3 to 195 d. Upon trial completion, calves were returned to their respective farms. Milk replacer options included varying protein level and amounts fed but in the majority of studies calves were fed a 20% CP: 20% fat MR at 0.57 kg/calf daily. Most calves (93%) were weaned at 6 wk. Milk replacer DM intake, starter DM intake, ADG, and BW at 8 wk were: 21.7 ± 2.5, 44.4 ± 12.0 kg, 0.63 ± 0.12 kg/d, and 75.8 ± 8.4 kg, respectively. Average age at first calving and first lactation 305-d milk yield were: 715 ± 46.5 d and 10959 ± 1527 kg, respectively. Separate mixed model analyses were conducted using the REML model fitting protocol of JMP (SAS) to determine the effect of birth season on 8 wk starter intake, BW, and ADG, and on first-lactation 305-d milk, milk fat, and true protein yield. Birth season, calving season, calving yr, and calving yr nested within herd were included in the models with calf trial as a random effect. Eight wk ADG and 8 wk ADG x birth season were also included when evaluating first-lactation performance. Calves born in fall and winter had greater (P < 0.05) starter intake (48.3 vs. 42.8 kg), BW (77.5 vs. 75.1 kg), and ADG (0.66 vs. 0.63 kg/d) at 8 wk. However, calves born in summer produced more 305-d milk during their first lactation than those born in the fall and winter (P < 0.05). There was no interaction between birth season and 8 wk ADG on first lactation performance.
Keywords: birth season, early life growth, first lactation