Effects of supplementing narasin to Bos indicus heifers during late-gestation and lactation on development of the offspring.

This experiment evaluated the effects of supplementing narasin during late-gestation and lactation on productive and physiological responses of Bos indicus beef heifers and their offspring. Pregnant, nulliparous Nelore heifers ( N = 88) that conceived under the same fixed-time artificial insemination protocol and to the same sire were used. Heifers were ranked by maternal ability genomic score, body weight ( BW ) and body condition score ( BCS ) and allocated to 44 drylot pens (2 heifers per pen; 10 × 25 m). Pens were ranked by these traits and alternatively assigned to receive ( NAR ) or not ( CON ) 0.260 mg of narasin/kg of heifer BW daily (Elanco Saúde Animal, São Paulo, Brazil). Narasin was mixed into a supplement offered at 0.30% of heifer BW from day 0 until heifers weaned their calves (day 316), whereas CON heifers received the same supplement without narasin addition. Heifers received Urochloa brizantha hay and water for ad libitum consumption (days 0 to 316) and calved between days 97 to 112 of the experiment. After calving, heifers and offspring had access to hay and supplement; hence, supplements and narasin were offered according to heifer + calf BW beginning on day 162. No treatment differences were detected ( P ≥ 0.18) for heifer BW and BCS during the experiment, although BW loss from day 0 to calving was less ( P = 0.04) in NAR compared to CON heifers. Hay intake during the experiment did not differ ( P = 0.79) between treatments. Serum IGF-I concentrations were greater ( P = 0.05) for NAR heifers on day 60 of the experiment and did not differ ( P ≥ 0.28) between treatments 24 h and 30 d after calving (treatment × day interaction; P = 0.04). No treatment effects were detected ( P ≥ 0.58) for calf birth BW. Serum concentrations of total protein 24 h after birth were greater ( P = 0.04) in calves from NAR compared with CON heifers, and a tendency ( P = 0.10) for a similar outcome was noted for serum IgG concentrations. Diarrhea incidence did not differ ( P = 0.16) between treatments, although the number of total diarrhea cases per calf were greater ( P = 0.03) in the CON offspring. Growth rate of calves from NAR heifers tended ( P = 0.08) to be greater, resulting in heavier calves at weaning ( P ≤ 0.04) compared with CON offspring. Collectively, these outcomes indicate narasin supplementation to beef heifers as a nutritional alternative to improve cow-calf productivity via developmental programming effects during gestation, as well as direct consumption by their nursing offspring.