The influence of offering a salt-limited protein supplement with or without a salt-limited mineral to beef cattle grazing Summer/Fall dryland pastures

Abstract

Beef cattle producers on rangelands often utilize supplements to meet protein and mineral nutrient requirements of beef cattle when the forage resource is high in fiber and low in crude protein and mineral nutrition. These supplements are often offered free choice, relying on sodium chloride as an intake modulator. However, it is unknown how offering multiple salt-containing supplements influences intake of one another. A supplement intake study was performed to observe the effects of offering multiple salt-containing supplements on intake behavior of each supplement and subsequent animal performance of yearling heifers at the Fort Ellis Research and Teaching Farm in Bozeman, Montana. Three treatments were offered in a complete randomized design utilizing a SmartFeed Pro feeding station during the summer-fall grazing period over two consecutive years: 1) ad libitum 25% NaCl protein pellet only; 2) ad libitum 25% NaCl loose mineral; and 3) ad libitum access to both salt-containing supplements. Heifer supplement intake displayed a treatment x period x year interaction (P < 0.01). Mineral-only heifers generally exhibited greater mineral intake (kg/day; g/kg BW; P < 0.01) compared to heifers consuming both salt-limited supplements in periods 2 and 3 of year 1 and all three periods of year 2. Meanwhile, there were generally no treatment differences in protein supplement intake between protein-only heifers and heifers consuming both salt-containing supplements (P > or = 0.71). The temporal decline in forage crude protein and increase in forage fiber content in year 1 likely contributed to differences in voluntary protein intake across periods. Meanwhile, differences in voluntary protein intake between years 1 and 2 of the study may be explained by environmental characteristics, with voluntary protein intake increasing quadratically throughout year 1 as forage crude protein and fiber remained stable across periods in year 2 when forage quality did not decrease. In conclusion, our results indicate that the providing multiple salt-containing supplements (protein and mineral) may reduce intake of loose mineral salt and that voluntary protein supplement intake and variation may be influenced more by environmental / temporal conditions.