The impacts of supplementing rumen degradable or undegradable protein to heifers and cows on supplement intake behavior, performance, reproduction, and nutrient digestion

Abstract

Low-quality forages, often low in protein, are a common feed resource for beef cattle in Montana and the western United States. A supplement intake study, as well as a digestion study were performed to observe the effects of rumen degradable protein (RDP) and rumen undegradable protein (RUP) on supplement intake behavior, performance, reproductive parameters, nutrient digestion, and rumen kinetics. Yearling heifers were used in a completely randomized design and two- and three-year old cows were used in a randomized complete block design for an 84-d supplement intake study. Treatments were: 1) pressed supplement block containing RUP (RUP), and 2) pressed supplement block containing RDP (RDP). Heifer and cow supplement intake displayed (P < 0.01) a treatment x period interaction. Cow intake rate and coefficient of variation displayed (P < 0.01) a treatment x period interaction. The RUP heifers consumed supplement faster (P < 0.01) than RDP heifers. The RDP cows had greater (P < 0.01) average daily gains than RUP cows. The RUP cows had greater final pregnancy rates than RDP cows (P = 0.04). In conclusion, protein type impacted intake behavior in cows and heifers, and RDP cows had ADG, but protein type did not negatively impact final performance or pregnancy success. Eight two-year old and eight three-year old rumen fistulated cows were used in a 2 x 2 factorial design for a 22-d digestion study. Animals were fed an ad libitum low-quality diet. Supplements included either RDP or RUP and were self-fed (SF) salt-limited pressed blocks or hand-fed (HF) the same loose ingredients without salt resulting in 4 dietary treatments: 1) RUP-SF, 2) RUP-HF, 3) RDP-SF, and 4) RDP-HF. There was a delivery x protein type interaction (P ? 0.04) for both NDF digestibility and water intake. There was an effect (P = 0.02) of protein type on fluid flow rate. Ruminal ammonia displayed (P < 0.01) a delivery x protein type x hour interaction. Valerate ruminal concentrations were greater in RDP supplemented animals compared to RUP supplemented animals (P = 0.04). In conclusion, self-fed supplements containing RDP may enhance the use of low-quality forages.