Antepartum high dietary supply of calcium affects bone homeostasis and offspring growth in dairy sheep and dairy goats

Abstract

This study investigated the effects of high dietary Ca supplementation during the final 21 days antepartum on Ca and bone homeostasis in dairy sheep and goats, and the growth response of their suckling offspring. Multiparous dairy sheep (n=5/group, 10 animals total) and goats (n=6/group, 12 animals total) were randomly assigned to 2 experimental groups. Feeding occurred restrictively (2.3 kg DM/d*animal^-1 antepartum for both species; 2.9 and 3.1 kg DM/d*animal^-1 for sheep and goats postpartum, respectively) according to recommendations with the exception of Ca during antepartum, where 1 group received a high Ca diet with CaCO₃ (1.3% in DM; 2.49fold recommendations) based on hay and concentrate 3 weeks antepartum, and the other group received no extra Ca on top (0.6% in DM; 1.15fold recommendations). Experimental feeding ended with parturition and animals were henceforth fed according to Swiss recommendations for lactating sheep and goats and kept together with their suckling offspring. The observation period spanned from 21 days antepartum to 56 days postpartum. Animals were subject to continuous veterinary surveillance and monitored for signs of milk fever. Data collection comprised quantitative and functional parameters of Ca and bone homeostasis as well as birth weights and daily weight gain of suckling lambs and kids. Data was analyzed by repeated measures and endpoint mixed models. The results of quantitative markers indicated that high dietary Ca antepartum significantly increased fecal Ca concentrations until parturition, suggesting efficient physiological mechanisms to manage Ca overload by increasing fecal excretion. No significant differences were observed in serum Ca levels, urinary Ca excretion, or bone mineral density between antepartum Ca feeding groups at any point in time of observation, indicating stable Ca homeostasis despite the dietary challenge. Species-specific differences in quantitative markers were noted including serum and colostral Ca levels as well as bone mineral density and mostly reflected results from earlier comparative studies. Serum 1,25-(OH)₂ vitamin D (calcitriol) as well as markers of bone formation and resorption were monitored, revealing significant increases in serum osteocalcin postpartum in goats and sheep fed high Ca antepartum. All other serum markers including calcitriol were not affected by the feeding regime but again by the species of animal, in line with previous works. All repeated measures were significantly affected by time except for urinary Ca and bone specific alkaline phosphatase activity in serum. Offspring of sheep and goats in the high Ca group exhibited significantly reduced average daily weight gain compared to the 0.6 % in DM Ca group, despite similar birth weights. We conclude that while dairy sheep and goats effectively managed high dietary Ca intake without overt signs of hypocalcemia or milk fever under the present experimental conditions, there were notable impacts on offspring growth and potential long-term physiological effects that require further research. These findings contribute to the understanding of mineral nutrition in late gestating dairy goats and sheep and stresses the need for further research on balanced dietary strategies to optimize health and productivity of lactating animals and their offspring.