Undegraded intake protein supplementation: II. Effects on plasma hormone and metabolite concentrations in periparturient beef cows fed low-quality hay during gestation and lactation

Hereford x Angus cows (n = 36; initial wt 568 +/- 59 kg) were used to evalu ate the effects of undegradable intake protein (UIP) supplementation on pla sma hormone and metabolite concentrations. Treatments were control (unsuppl emented) or one of three protein supplements. Supplements were fed at 1.3 k g DM/d and included UIP at low, medium, or high levels (53, 223, or 412 g U IP/kg supplement DM, respectively). Supplements were formulated to be isoca loric (1.77 Meal NEm/kg) and to contain equal amounts of degradable intake protein (DIP; 211 g DIP/kg supplement DM). Prairie hay (5.8% CP) was offere d for ad libitum consumption. Jugular blood samples were collected daily fr om each cow during six 7-d collection periods (corresponding to mo 7, 8, an d 9 of gestation and to mo 1, 2, and 3 of lactation). Plasma glucose concen trations were similar between control and supplemented cows during mo 2 and 3 of lactation; however, the low UIP treatment group had consistently high er plasma glucose (P less than or equal to .02) than cows fed medium or hig h UIP supplements during gestation and the last month of lactation. During gestation, cows fed the high UIP supplement had higher (P less than or equa l to .08) plasma glucose than cows fed the medium UIP supplement. During ge station, plasma insulin concentration was increased (P = .01) by supplement ation; insulin also increased (P < .01; mo 8 and 9) as supplemental UTP inc reased. During lactation, plasma insulin was greater (P = .01) in supplemen ted than in control cows. During mo 2 and 3 of lactation, insulin was lower (P less than or equal to .04) in cows fed low UIP supplement compared with cows fed medium or high UIP supplements. Growth hormone concentration was higher (P less than or equal to .03) in control cows than in supplemented c ows in all periods measured except mo 7 of gestation. Plasma nonesterified fatty acid concentrations were higher (P 1:.03) in control cows than in sup plemented cows in all periods measured except the Ist mo of lactation. Thes e data are interpreted to suggest that protein supplementation and level of UIP can alter plasma concentrations of hormones and metabolites in gestati ng and lactating beef cows consuming low-quality hay.