Salt limited intake: impacts of salt level and form of supplement on intake, nutrient digestion, and variability of supplement intake in beef cattle
White, Hayley Christina
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For centuries, salt has been used as a cost effective intake-limiter of supplements for ruminants. Beef cattle production in the western United States relies on self-fed, salt-limited supplement to offset seasonal nutrient deficiencies which, in turn, may improve performance and increase forage intake. However, research has found high variation in individual supplement intake among animals and across days. If cattle are over consuming high-salt diets, this may result in negative impacts on animal performance and additional cost for the producer. Two studies were conducted to evaluate the effects of form of supplement on supplement intake behavior, body weight, and body condition change and the impacts of supplemental salt levels on forage intake, water intake, dry matter digestibility, and rumen fermentation of yearling heifers consuming low quality forages. During a two-year summer grazing trial, individual supplement intake, time spent at the feeder, and frequency of visits was measured. It was found that supplementation and form of supplement did not influence heifer weight gain or intake CV (P = 0.26), but heifers in the pelleted treatment consumed more supplement (grams/kg BW), and at a faster rate compared to heifers fed the loose supplement form (P < 0.01). In study 2, six ruminally cannulated heifers were assigned to treatments to determine the effect of salt levels on digestibility and rumen parameters. Salt treatments consisted of: 1) control, no salt (CON), 2) 0.05% of BW salt (LOW), and 3) 0.1% of BW salt (HIGH). Forage and water intake, digestibility, and rumen parameters were measured. Supplemental salt tended to decrease forage intake (grams/kg BW; P = 0.06) and tended to increase DM fill (P = 0.07). Both water intake and liquid fill increased with increasing level of salt (P < 0.01). Ruminal pH and ammonia levels decreased with increasing salt (P < 0.01) while acetate concentration increased (P < 0.01). Digestibility was not influenced by salt levels (P > 0.05). Our results suggest that pelleting salt-limited supplements has a masking effect on the intake regulation of salt. Additionally, increasing levels of salt modifies rumen fermentation and digestion suggesting lower efficiency of intake and use with high-salt diets.