Investigating the interaction between body condition at calving and pre-calving energy and protein nutrition on the early lactation performance of dairy cows
Australian Journal of Experimental Agriculture 45(12): 1507-1518
The experiment was an investigation into the interaction between body condition at calving and the provision of additional dietary energy or protein to a total mixed ration (TMR) in late gestation on milk production and indices of reproductive performance. Seventy-two Holstein - Friesian multiparous cows ( 12 per treatment) were fed to achieve target body condition scores (BCS) of either 4 (3.5 - 4.5) or 6 (5.5 - 6.5) units by 1 month before they calved ( July). They were individually fed 1 of 3 diets during the last 26 (s. d. +/- 7.4) days before calving date ( mean of 19 August; s. d. +/- 9.7). The 3 diets were ( 1) a TMR containing maize silage, barley grain, canola meal and hay, fed at 1.5% of liveweight ( control diet), ( 2) the TMR plus 3.5 kg DM of wheat-based pellets ( energy diet), and ( 3) the TMR plus 3.1 kg DM of soyabean meal ( protein diet). Cows grazed highly digestible pasture after calving at pasture allowances of about 35 kg DM/cow. day, and were supplemented with 6 kg DM of cereal grain-based pellets per day. Cows were fed this diet for an average of about 10 weeks, from calving until the start of mating at the end of October. The provision of additional dietary energy and protein before calving did not affect post-partum production, and there were no interactions with body condition. On average, the BCS 6 cows were 111 kg heavier (P< 0.05), and were 1.8 units of body condition higher ( P< 0.05), than the BCS 4 cows. The thin cows maintained body condition during the month before parturition while the fat cows lost condition. The cows offered additional protein improved their body condition (+ 0.07 units) during this time, while the cows in the other 2 dietary treatments lost condition ( - 0.10 units). Average daily rumen fluid pH was lowest in the cows fed the additional energy. Blood urea and rumen fluid ammonia concentrations were increased markedly by feeding the protein diet. In comparison with cows offered the control and energy diets, the cows offered additional protein had the highest ( P< 0.05) urine pH levels (6.24 v. 5.64 and 5.59 for the protein, control and energy diets, respectively), the lowest ( P< 0.05) blood serum concentrations of calcium at calving (1.74 v. 2.06 and 1.99 mmol/L for the protein, control and energy diets, respectively), and tended to have more milk fever and retained foetal membranes. Regression analysis indicated that the response to improving BCS at calving was 1.1 kg milk per additional BCS at calving ( P< 0.05), and the fatter cows produced milk with a higher ( P< 0.05) milk fat concentration (3.46 v. 3.07%) than the thinner cows. There was no effect (P> 0.05) of treatment on days to first ovulation or in-calf rates although only about 80% of cows conceived during the 12-week mating period.