The impact of early life nutrition and housing on growth and reproduction in dairy cattle.

Contentious issues in calf rearing include milk feeding practices and single versus group housing. The current study was performed on a high producing 170 Holstein cow dairy farm, to investigate the impact of nutrition and housing on growth and reproduction. Heifer calves (n = 100) were allocated in birth order to one of two commonly used management strategies. All calves received 3-4 litres of dam specific colostrum within 6 hours of birth. Group A calves were group housed from birth and fed milk replacer (MR) ad libitum via a computerised machine utilising a single teat, with weaning commencing at 63 days of age. Group R calves were initially housed in individual pens and received 2.5 litres of MR twice daily via a bucket until 21 days of age when they were group housed and fed 3 litres of MR twice daily via a group trough with weaning commencing at 56 days. From 12 weeks of age onwards, calves in both dietary groups were subject to common nutritional and husbandry protocols. All breeding of heifers was via artificial insemination with no hormonal intervention. Calves were weighed, body condition scored and morphometric measures recorded weekly up till 12 weeks of age then monthly until conception. Pre-weaning growth rates (kg/day) were significantly higher in Group A calves compared to Group R (0.89, 95% CI 0.86-0.93 vs 0.57, 95% CI 0.54-0.6 kg/day P < 0.001) with the most marked differences observed during the first three weeks of life (0.72, 95% CI 0.61-0.82 vs 0.17, 95% CI 0.08-0.26 P < 0.001). Whilst Group A calves gained body condition score (BCS) throughout the pre-weaning phase, Group R calves lost BCS during the first 4 weeks of life. Data suggested that Group R calves supported skeletal growth during this period by catabolising body tissue. Group A calves had a greater risk of disease than group R calves during the pre-weaning phase (diarrhoea: odds ratio 3.86, 95% CI 1.67-8.9; pneumonia: odds ratio 5.80, 95% CI 2.33-14.44) although no calves died during this period. Whilst pneumonia had a significant impact on growth during the study duration (P = 0.008), this was not the case for diarrhoea. Whilst univariate analysis failed to show any statistically significant group differences (P > 0.050) in any of the mean values of measured reproductive parameters, multivariable Cox regression suggested that there was a weak trend (P = 0.072) for Group A animals to achieve first service earlier than their Group R counterparts (62.6 weeks versus 65.3 weeks). Irrespective of dietary group, the hazard for achievement of all measured reproductive parameters, apart from time to puberty, was 20-40% less for heifers borne from multiparous dams compared to heifers from primiparous dams