Abstract
Two trials have been carried out to evaluate welfare implications or rbST treatment in dairy cows. 1st trial: effects of rbST and F/C ratio on milk production traits, reproductive, metabolic and endocrine parameters were examined. Forty Italian Holstein Friesians (70 d post-partum) were divided into 4 groups: low concentrate (LC); high concentrate (HC); LC+rbST; HC=rbST. LC and HC groups were fed 0.35 and 0.50 kg concentrate/kg of milk yield >18kg. rbST (640 mg/cow) was injected at 28 d intervals for 112 d. 2nd trial: 4 dairy cows (191 d post-partum), each fitted with rumen cannula, were used in a crossover design to examine influence of rbST (640 mg/28 d) on rumen parameters. There was an average increase of 19% in 4% FCM for rbST versus control cows (24.6 vs. 21.0; 18.33 vs. 15.15 kg/d). Milk composition was unaffected except for a decrease (P<0.01) in milk protein percentage of LC+rbST group (2.87% vs. 2.94%). Days open were unaffected by rbST. Seven days post-injection, rbST significantly increased plasma GH, glucose, NEFA, triglyceride, phospholipid, insulin, somatostatin, lowered plasma urea and did not affect plasma total protein, albumin and total cholesterol. Somatotropin did not influence ruminal pH (6.08 vs. 6.10), concentrations of ruminal ammonia (8.28 mg/100 ml vs. 10.48 mg/100 ml), trotal ruminal VFA (111.73 mmol/1 vs. 114.09 mmol/1) and their molar proportion and liquid passage rate (14%/h).
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