EFFECTS OF AVOPARCIN AND BOVINE SOMATOTROPIN ON MEASURES OF PRODUCTION AND REPRODUCTION IN DAIRY-COWS

The objective was to determine the effects of avoparcin, bovine somatotropin (bST) and the additive effects of both avoparcin and bST on milk yield, milk composition, live-weight changes and reproduction parameters in post partum dairy cows. Forty-eight autumn calving cows were allocated using a split-plot within randomized complete-block design to the following treatments: (i) control (2 mi saline plus 1 kg untreated concentrate per day); (ii) avoparcin (2 mi saline pills 1 kg concentrate containing 100 mg avoparin per day); (iii) bST (25 mg bST in 2 mi saline plus 1 kg untreated concentrate per day); and (iv) avoparcin plus bST (25 mg bST in 2 mi saline plus 1 kg concentrate containing 100 mg avoparcin per day)) All injections were given subcutaneously and treatment continued for 84 clays beginning 55 (s.e. 4) days after calving. The cows were offered grass silage ad libitum supplemented with 72 kg cereal-based concentrates daily. Milk yield and milk composition were measured thrice and once weekly, 1 espectively. The cows were weighed and body condition score was assessed every 2 weeks. Mean daily milk yield of cows assigned to control teas 20 1 (s.e. 1.5) kg, avoparcin, 21.5 (s.e. 1.5) kg, bST, 23.9 (s.e. 20) kg and avoparcin plus bST, 25.2 (s.e. 22) kg over the 84 days of the trial. bST increased milk yield proportionately by 0.18 compared ed with all cows not given bST (P < 0.01). Avoparcin did not significantly increase milk yield. There tons no effect of any treatment on milk composition, body weight or body condition score. None of the experimental treatments had any effect on calving to first service interval, calving to conception interval, number of services pel conception or overall conception rate. These results show that in early lactation, avoparcin alone had no effect on production or reproduction parameters in dairy cows; bST alone increased milk yield but did not affect any other production or reproduction parameter. There teas no significant additional increase in milk yield when avoparcin and bST were given in combination, compared with bST alone.