ABOMASAL INFUSION OF GLUCOSE AND FAT - EFFECT ON DIGESTION, PRODUCTION, AND OVARIAN AND UTERINE FUNCTIONS OF COWS

Four ruminally cannulated lactating dairy cows, arranged in a 4 x 4 La tin square design, were infused abomasally with 1) water (control), 2) 1 kg/d of glucose, 3) 0.45 kg/d of tallow, and 4) 0.45 kg/d of yellow grease. Cows were synchronized for estrus within each 35-d period by injection of a GnRH agonist followed 7 d later by an injection of PGF( 2 alpha). Dry matter intake was not affected by infusates. Apparent di gestibility of total fatty acids was greater for cows receiving the fa t infusions relative to those receiving the glucose infusion and tende d to increase for cows receiving the yellow grease infusion compared w ith those receiving the tallow infusion. Energy infusions decreased ap parent acid detergent fiber digestibility compared with effects of the control infusion. Fat infusions tended to increase milk fat percentag e and decrease the energy status of cows relative to the glucose infus ion. The feed efficiency was greater for cows receiving fat infusions than for those receiving the glucose infusion and was greater for cows receiving the yellow grease infusion than for those receiving the tal low infusion. Plasma progesterone concentration peaked higher during t he estrous cycle for cows infused with fat than for those infused with glucose. Mean growth rate and maximum size of the first wave dominant follicle were greater with tallow than with yellow grease. During the period of infusion of yellow grease and afterward, release of 13,14-d ihydro-15-keto-PGF(2 alpha) in response to an injection of oxytocin on d 15 of the estrous cycle was attenuated.