THE EFFECT OF PREPARTUM AND POSTPARTUM ENERGY AND PROTEIN SUPPLY ON THE BLOOD METABOLITES AND REPRODUCTIVE-PERFORMANCE OF SINGLE-SUCKLING AND TWIN-SUCKLING BEEF-COWS

Changes in certain blood metabolites, serum pr progesterone concentrat ion and pregnancy rate, were monitored for single- and twin-suckling c ows in two experiments. In experiment 1, cows were managed to achieve condition scores at calving of 2.1 (low) and 3.1 (moderate). Subsequen tly, these animals were placed on a fixed level of energy intake (80 M J metabolizable energy (ME) per day) for 16 weeks. Post-partum diets c ontained differing amounts of digestible undegradable protein (DUP), b ut similar amounts of effective rumen degradable protein (ERDP). In ex periment 2, all cows were fed to achieve a condition score at calving of around 2.75. These animals were subsequently placed on two levels o f energy intake (80 MJ and 130 MJ ME per day) for 16 weeks. The diets providing these levels of energy intake also contained differing amoun ts of DUP. Pregnancies were established by embryo transfer following i nduced oestrus. Cows in moderate body condition at calving subsequentl y had higher (P < 0.05) serum non-esterified fatty acid (NEFA) concent rations. Cotes on 130 MJ ME per day had lower serum NEFA concentration s than cotes on 80 MJ ME per day. Cows given higher DUP diets had high er (P < 0.05) serum NEFA concentrations when in negative energy balanc e and lower serum NEFA concentrations when close to energy equilibrium than cows given lower DUP diets. Twin-suckling cotes had higher (P < 0.05) serum NEFA concentrations than single-stickling cotes, but only during the first 3 weeks post partum. Plasma glucose concentrations we re below 3 mmol/l for twin-suckling cows until week 7 post partum when they became similar to the values for single-suckling cows. Serum D-3 -hydroxybutyrate concentrations mirrored those of plasma glucose. Seru m urea-nitrogen concentrations were high for twin-suckling cows on 80 MJ ME per day and single-suckling cows on 130 MJ ME per day. Neither b ody condition at calving nor post-partum energy intake significantly i nfluenced the time taken for cows to overcome anovulation nor did they significantly influence the proportion of cows which eventually resum ed normal oestrous cyclicity. DUP concentration in the post-partum die t had no overall effect on the various measures of fertility assessed but thin cows at calving subsequently placed on the high DUP diet took longer to ovulate (55 days; P < 0.05) and had the lowest pregnancy ra te (0.30). The post-partum anovulatory period was longer (P < 0.01) by 27 days in experiment 1 and 12 days in experiment 2 for twin-suckling cows compared with single-suckling cows. A lower proportion (P < 0.00 1) of twin-suckling cows regained oestrous cyclicity and became pregna nt in experiment 1. Fertility traits were improved when twin-suckling cows were in moderate body condition at calving and/or offered 130 MJ ME per day during the post-partum period.