Influence of source and amount of dietary protein on performance, blood metabolites, and reproductive function of primiparous beef cows2

Abstract

Forty Angus x Hereford 2-yr-old primiparous cows (358 kg) were used to determine the effects of source and amount of CP on performance, reproductive function, and metabolic status of suckled primiparous cows. A 2 x 2 factorial treatment arrangement was used; cows received either 100 or 150% of NRC recommendations for CP in diets that contained either soybean meal (low escape = L) or corn gluten meal/blood meal (high escape = H) as the principal supplemental protein source. Resulting treatments were 100-L, 100-H, 150-L, and 150-H. Cows were individually fed diets for 100 d or until they were observed to be in standing estrus. Diets were isoenergetic and limit-fed to meet NRC recommendations for NE, Ca, and P for 364-kg, 2-yr-old primiparous cows producing 4.5 kg of milk daily and gaining .23 kg/d. Increased CP tended (P = .09) to increase ADG in cows, but body condition score was unaffected. Increased CP and use of a CP source with higher potential for ruminal escape increased ADG in calves from d 0 to 97 (P = .002 and .04, respectively), which corresponded with numerical changes in milk production. Feeding high escape CP sources decreased plasma glucose and urea N (P = .04 and .0001, respectively). Increased CP tended (P = .12) to increase plasma glucose and increased (P = .0001) plasma urea N. Treatment had no effect on profiles of LH or progesterone. Although numerical differences in conception rate seemed large for 100-L compared with the remaining treatments, statistical significance was not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of post-calving supplemental protein on calf performance and reproductive efficiency for beef cows fed silage

“…The effect of supplemental protein for beef cows has mostly been examined in cows fed basal diets containing considerably less CP than in our trials (De Gracia and Ward 1991;Rusche et al 1993;Triplett et al 1995). In our trials protein intake from silage alone was at least 20% in excess of NRC (1996) requirements; therefore, a response to protein should not have been observed for any level of supplementation.…”

“…This suggested that the response by cows was from the UIP, rather than from the overall increase in CP concentration. Other research has also shown responses to UIP supply up to a certain level (Blasi et al 1991;De Gracia and Ward 1991;Rusche et al 1993;Triplett et al 1995). On silage-based diets, this can be attributed to low metabolizable protein supply, possibly due to a highly degradable protein source combined with a lack of energy available to rumen microbes for microbial protein synthesis (AFRC 1990).…”

“…In their study, cows grazing smooth brome (Bromus inermis) were supplemented with a highly undegradable protein supplement based on CGM and blood meal. Other research has observed a positive relationship between level of UIP and cow weight gain (Wiley et al 1991;Dhuyvetter et al 1993;Rusche et al 1993). However, in those studies energy intake of cows was restricted, either by limit feeding or by forage quality.…”

“…Indeed, many research trials fail to find significant effects on BCS, because of the small differences relative to the experimental variation of this parameter (Rusche et al 1993). When the treatment means for BCS in both trials are plotted against ME intake (Fig.…”

“…Rusche et al (1993) showed that calf performance can be improved when the dam is fed extra protein, especially if it is of low degradability. Research with dairy cows has clearly shown that supplementation with protein of low to moderate degradability can increase milk yield, especially when the ration is silage based (Robinson et al 1992).…”