Effects of pelleted versus loose salt-limited protein supplement on supplement intake behavior of yearling heifers grazing dryland pastures

Abstract

Abstract The objectives of this study were to evaluate the impacts of supplement form on supplement intake behavior, body weight (BW), and body condition score (BCS) change of yearling heifers grazing dryland pastures during the summer. In each of the two years, Angus crossbred heifers (14 mo of age; year 1, N = 57, BW = 449 ± 3.60 kg; year 2, N = 58, BW = 328 ± 3.57 kg) were used in a 84-d completely randomized design evaluating the following treatments: 1) control, no supplement; 2) salt-limited supplement in pelleted form; and 3) a salt-limited supplement in loose form. Individual supplement intake, and time spent at the feeder were measured throughout the course of the study using a SmartFeed Pro self-feeder system (C-Lock Inc., Rapid City, SD, USA). On days 0, 42, and 84, the heifers were weighed, and body condition scored following a 16-h shrink. Supplementation and form of supplement did not influence (P ≥ 0.62) BW change for yearling heifers within or across study grazing periods. Body condition score was not influenced (P ≥ 0.26) by supplementation and form within the 0 to 42 (period 1) or 42 to 84 (period 2)-d periods but displayed a treatment by year interaction (P < 0.01) for the 84-d summer grazing period. Supplement intake (kg/d and g/kg BW) displayed a treatment × period interaction (P < 0.01). Supplement intake (kg/d) of heifers consuming pelleted supplement was 28% and 31% greater (P ≤ 0.02) than heifers consuming loose supplement in periods 1 and 2, respectively. Supplement intake (g/kg BW) of heifers consuming pelleted supplement was 24% and 32% greater (P ≤ 0.05) than heifers consuming loose supplement in periods 1 and 2, respectively. Overall, across both years, supplement intake in period 1 was less than half (P < 0.01) that of period 2, averaging 0.50 and 1.14 kg/day, respectively. Variation in supplement intake (% CV) was greater (P = 0.03) in period 1 compared to period 2, averaging 119% and 91%, respectively. In addition, variation in supplement intake was greater (P = 0.03) in year 2 than year 1, averaging 122% and 88%. Our results suggest that salt-limited supplements have a high degree of intake variation and pelleting could have a masking effect as indicated by the greater intake and intake rate of supplement with heifers consuming the pelleted supplement.