PSXII-11 - Impact of pre-breeding and breeding supplementation in May-born range heifers on growth rates and reproductive performance

Abstract: Our objectives were to determine the impact rumen undegradable protein (RUP) supplementation prior to and during the breeding season had on growth rates and reproductive performance in May-born yearling range heifers. This study was conducted over a three-year period at the University of Nebraska, Gudmundsen Sandhills Laboratory (GSL) near Whitman, NE and utilized May-born Red Angus x Simmental crossbred heifers (n = 192; weaning body weight (BW) = 200 kg + 28 kg). Heifers were randomly assigned by pre-breeding BW to one of two treatments: 1) received 0.908 kg of a dried distillers grain supplement (DDGS; Supp, n = 66) pre-breeding through the breeding season or 2) received no supplement (NoSupp, n = 138). Each year, treatments were initiated in July and ended in August (55-d + 3). Using a C-Lock Smart Feeder (Rapid City, SD) heifers had individual access to their allotted DDGS supplementation. On average, NoSupp heifers consumed 0.09 kg/d (year 1) and 0.02 kg/d (year 2 and 3), whereas, Supp heifers averaged 0.59, 0.74, and 0.76 kg/d in year 1, 2, and 3, respectively. Heifer BW was collected pre-trial (May), pre-breeding (July), breeding (August), pregnancy diagnosis (October), and pre-calving (April). Body condition score (BCS) was collected at pregnancy diagnosis (October) and pre-calving (April; Year 1 and 2). Before each breeding season, two blood samples were collected 10-d apart to determine pubertal status. Heifers were synchronized with a single 5ml intramuscular injection of prostaglandin F2 alpha (Lutalyse, Zoetis, Parsippany, NJ) 5-d after bull turnout during a 30 d natural service breeding season. Pregnancy diagnosis was determined via rectal ultrasound in October. No differences (P ³ 0.12) in BW were noted among treatments for all measurement timepoints. Moreover, SUPP heifers had greater (P £ 0.02) average daily gain (ADG) from pre – trial to pregnancy diagnosis compared to NoSUPP heifers. However, there was no differences (P = 0.11) in ADG from pregnancy diagnosis to pre – calving. At pregnancy diagnosis (October), a treatment x year interaction (P = 0.02) for BCS was present where Supp heifers had a greater BCS than NoSupp heifers in year 3. Heifer BCS pre – calving was not affected (P = 0.12) by treatment. There was a greater percentage (P < 0.01) of SUPP heifers cycling compared to NoSUPP heifers. However, there were no differences (P ³ 0.24) in pregnancy rates, the percentage that calved in the first 21 d, calf birth BW, or subsequent calving date. Ultimately, this study implies that providing a RUP supplement prior to and during the breeding season will increase the percentage of heifers that are cycling before breeding and have a greater ADG through pregnancy diagnosis, however, supplementation will not impact other reproductive parameters or BW gains.