THE EFFECT OF PREPARTUM AND POSTPARTUM ENERGY AND PROTEIN SUPPLY ON THE PERFORMANCE OF SINGLE-SUCKLING AND TWIN-SUCKLING BEEF-COWS AND THEIR CALVES

Changes in live weight, body condition, milk production and compositio n were monitored for single- and twin-suckling cows in two experiments . In experiment 1, all cows were managed for 3 months before calving t o achieve condition scores at calving 2.1 (low) and 3 1 (moderate). Su bsequently, these animals were placed on a fixed level of energy intak e (80 MJ metabolizable energy (ME) per day) for 16 weeks. Post-partum diets contained differing amounts of digestible undegradable protein ( DUP), but similar amounts of effective rumen degradable protein (EXDP) . In experiment 2, single- and twin-suckling cows were fed to achieve a condition score at calving of around 2.75. These animals were subseq uently placed on two levels of energy intake (80 MJ and 130 MJ ME per day) during the first 16 weeks of lactation. The diets providing these energy intakes also contained differing amounts of DUP. Neither the l evel of DUP in the diet nor the level of feeding significantly altered the digestibility of the dry matter or organic matter in the dry matt er of the experimental diets. Body condition at calving had little eff ect on daily milk yield (9.5 kg) and composition (33.5 g/kg fat; 30.0 g/kg protein) in experiment 1. Cows with higher body condition scores at calving lost 13.5 kg more live weight and 0.26 units more body cond ition (P < 0.05) during the 1st month post partum but remained in bett er condition throughout the trial period than cows with lower body con dition scores. Cows on 130 MJ ME pel day produced higher (P < 0.001) d aily yields of milk, milk fat and protein (+2.0 kg; +151 g; +85 g) and lost 57 kg less live weight and 0.52 units less body condition (P < 0 .001) than cows on 80 MJ ME per day. Elevated dietary levels of DUP pr omoted (P < 0.05) daily milk yields (by 1.25 kg) and reduced live-weig ht and body condition-score loss during the Ist month post partum in b oth experiments. Twin-suckling cows produced the highest average daily yields of milk throughout the 16-week trial period in both experiment s but yields were not significantly higher after early lactation in ex periment 1. Cow body condition score at calving and the level of DUP i n the post-partum diet of cows had no effect on the post-partum perfor mance of carves, Twin calves had slower growth rates (P < 0.001) than single calves (0.65 and 1.07 kg/day respectively) in experiment 1. How ever, twin calves sucking cows on 130 MJ ME per day in experiment 2 gr ew similarly to single sticking calves from week 8 of lactation (0.8 k g/day).