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 somato tropin (bST) and the additive effects of both avoparcin and bST on mil k yield, milk composition, live-weight changes and reproduction parame ters in post partum dairy cows. Forty-eight autumn calving cows were a llocated using a split-plot within randomized complete-block design to the following treatments: (i) control (2 mi saline plus 1 kg untreate d concentrate per day); (ii) avoparcin (2 mi saline pills 1 kg concent rate 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 p lus bST (25 mg bST in 2 mi saline plus 1 kg concentrate containing 100 mg avoparcin per day)) All injections were given subcutaneously and t reatment continued for 84 clays beginning 55 (s.e. 4) days after calvi ng. The cows were offered grass silage ad libitum supplemented with 72 kg cereal-based concentrates daily. Milk yield and milk composition w ere measured thrice and once weekly, 1 espectively. The cows were weig hed and body condition score was assessed every 2 weeks. Mean daily mi lk yield of cows assigned to control teas 20 1 (s.e. 1.5) kg, avoparci n, 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 yi eld proportionately by 0.18 compared ed with all cows not given bST (P < 0.01). Avoparcin did not significantly increase milk yield. There t ons no effect of any treatment on milk composition, body weight or bod y 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 re sults show that in early lactation, avoparcin alone had no effect on p roduction or reproduction parameters in dairy cows; bST alone increase d milk yield but did not affect any other production or reproduction p arameter. There teas no significant additional increase in milk yield when avoparcin and bST were given in combination, compared with bST al one.