Effects of a low protein diet on calcium metabolism in growing Cashmere goats

Abstract

The aim of the present study was to determine the effects of a low-protein diet on calcium (Ca) homeostasis and the gene expression related to Ca absorption in the gastrointestinal tract and kidney in growing Cashmere goats. A total of 30 cashmere goats (approximately 4 months old and 15.51±2.3 kg live weight) were divided into a control (10.5%), low (7.5%), or high (13.5%) protein group, with 10 replicates in each group. The experiment was composed of a 15-d adaptation and a 42-d collection period. The low protein group had lower contents of urea, Ca, calcitriol, and insulin-like growth factor-1 (IGF-1) in the plasma and urea and Ca in urine, with substantially higher contents of parathyroid hormone in the plasma and creatinine in the plasma and urine at 21 d and 42 d. The mRNA expression of intestinal vitamin D-dependent 9 ku calcium binding protein (CaBP-D9k), plasma membrane calcium ATPase 1b, transient receptor potential vanilloid channel type 6 (TRPV6), and the protein expression of intestinal CaBP-D9k and TRPV6 in the low protein group were decreased, whereas the mRNA and protein expression of the vitamin D receptor were not affected. Goats fed a reduced-protein diet showed substantially higher amounts of renal water channel aquaporin 1 (AQP1) mRNA in cortical tissue, and the expression of AQP2 mRNA and protein was elevated in the outer medulla. In conclusion, changing dietary N intake affected Ca metabolism in growing Cashmere goats.