Methods for improvement of production efficiency in thermal stressed dairy cows

Abstract

Multiple studies were conducted to evaluate management options for cows in a thermal stress environment. Those options included cooling to enhance cow comfort, recombinant bovine somatotropin (rbST; Posilac®) to potentially increase milk production, and reproductive hormone scheduling to theoretically coordinate follicular growth leading to ovulation. In the first series of trials measuring the effects of cooling and rbST on milk yield, reproductive performance, and health in Jersey cows during two summer of thermal stress, cows were divided into on of two pens. Both Year 1 and Year 2 control cows (n = 143 and n = 183, respectively) were housed in a pen with no cooling other than shade. The cooled treatment cows each year (n = 142, n = 180) were housed in a pen utilizing the Universal Fog cooling system. One half of the cows in each group was assigned to receive rbST on d 63 postpartum (pp). Cows were assigned to the trial at various days pp, but no cow was assigned prior to d 63, coincident with commencement of rbST injections. The main effect for cooling in combination with rbST increased milk yield compared to no cooling and no rbST for 1999 and 2000 (25.5 vs 21.8 kg/d, and 23.7 vs 20.5, respectively; P < 0.05). Cooling and rbST effects on milk yield were additive the first year, but had a synergistic interaction the second year. Incidences of mastitis (8 vs 17; P < 0.05) for both years and laminitis (2 vs 7; P < 0.05) for Year 1 were both reduced. Reproductive performance was improved in cows given access to cooling (126 pregnant and 6 abortions) vs shade only (112 pregnant vs 13 abortions) in Year 1 (P < 0.05). Additional income over cooling cost was 67¢/cow per day for Year 1 and 52¢/cow per day for Year 2. In the second series of experiments, Holstein and Brown Swiss cows at 56 ± 3.5 d pp were used to evaluate ovulation rates over three seasons, including two summers when half the cows were cooled. All cows received rbST beginning d 63 ± 3.5 pp regardless of treatment. For Exp.1, 58 cows were assigned at calving, beginning June 1, 1999, to either a cooled (Korral Kool™) or non-cooled (shade only, control) pen. At d 56 ± 3.5 pp, all cows commenced a hormonal program coined Select Synch, comprised of an injection of GnRH (100 μg) agonist (Factrel®) followed 7 d later with an injection of PGF₂α (25 mg In-Synch™), at which time ultrasonography was initiated and continued until ovulation or follicular turnover. Experiment 2 was conducted the same as Exp. 1, with the assignment of cows starting Nov. 1, 1999. In Exp.3, all cows were assigned the same as Exp. 1 and 2 beginning June 1, 2000. At d 56 ± 3.5 pp, cows were scheduled to commence Ovsynch, which was identical to Select Synch, except a second Factrel® injection was administered 33 h after 35 mg Lutalyse®. Ultrasonography was the same as described above. Ovsynch led to a higher frequency of ovulations for the non-cooled and cooled cows (77.3 and 69.6%, respectively), than Select Synch for the non-cooled, cooled, and winter treatments (27.6, 24.1 and 29.4%, respectively). Ovulation frequencies were related more to hormonal programming rather than the season.