Suplementação de vacas leiteiras pré-parturientes com glicerina

Abstract

The objective was to test the effect of glycerin suplemenrtation before calving on productive and reproductive performance ofdairy cows. Experiment 1 was developed in two dairy farms, in the south of Minas Gerais. Forty-two multiparous and primiparous Holstein cows were used: 21 received a single glycerin oral dose (300ml/d) 7d before calving and 21 control were not treated. Milk production and fat content, interval from calving to lst service and to conception, number of services per conception and conception rate up to 150 days postpartum were analysed. In experiment 2 six cows fistulated open and non-lactaning cows were used. The treatments were glycerin, propyleneglycol and control. Infusions (300 ml) were done for three days, in a replicated 3x3 latin square design, with three days rest between each infusion. Infusions were done once a day. Rumen and blood samples were taken at 0, 0.5, 1.0, 1.5 e 2.0 h after infusion for pH and plasma insulin concentration analyses. Glycerin supplementation increased (P=0.04) milk production (24.0 vs 21.3 kg/d). Interaction between treatment and week was signifícant (P = 0.003). Parity affected (P=0.002), average production 19.0 ± 2.4, 24.4 ± 2.61 and 24.5 ± 2.6 kg/d, respectively for parities 1, 2 and >3, however, there was no interaction between parity and treatment. Milk fat content was afected by week (P=0.08), farm (P=0,001) and parity x treatment interaction (P=0,03). Glycerin supplementation apparently did not influence reproduction. In the experiment 2, plasma insulin concentration was different (P=0.10) for (11.1+2.1; 17.9+2.1 e 9.6±1.8 uUI/ml, respectively for glycerin, propyleneglycol and control). There was no interaction between treatment and time (P=0,37) for plasma insulin concentration. Plasma insulin concentration peaked at 1.5 hours for propyleneglycol (21.5+2.8 uUI/ml) and at 1 hour for glycerin (13.9+2.7 u-UI/ml) after infusion; control was stable after one hour (10.5+2.5 uUI/ml). Treatments did not affect (P = 0.90) ruminal pH. It can be concluded that glycerin supplementation in pre-partum dairycows may benefit milk production, probably by preventing ketosis.