Effects of excess dietary calcium supplementation during the transition phase on calcium and bone metabolism of dairy sheep and goats and growth response of their suckling offspring

This study investigated the effects of excess dietary Ca supplementation during the transition phase on Ca and bone metabolism in dairy sheep and goats, as well as the growth response of their suckling offspring. Multiparous dairy sheep (n=6/group) and goats (n=5/group) were randomly assigned to a control and treatment group. The experimental group received a high Ca diet (1.3% DM) based on hay and concentrate three weeks ante partum , compared to the control group (0.6% DM). Experimental feeding ended with parturition and animals were henceforth fed according to recommendations for lactating sheep and goats and kept together with their suckling offspring. The observation period spanned from 21 d ante partum to 56 d post partum. 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 metabolism 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 excess dietary Ca ante partum significantly increased fecal Ca concentrations until parturition by 2 log ₁₀ -orders of magnitude, 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 (BMD) between control and experimental groups at any point in time of observation, indicating stable Ca homeostasis despite the dietary excess. However, species-specific differences were noted, with sheep generally showing significantly higher serum and colostral Ca levels, as well as BMD, compared to goats. Serum calcitriol as well as markers of bone formation and resorption were monitored, revealing significant increases in serum osteocalcin post partum in goats and sheep fed high Ca ante partum . All other serum markers including calcitriol were not affected by the feeding regime but species of animal. Vitamin D receptor abundance in goats’ colonic mucosa were numerically lower during parturition when high Ca was fed. 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 control, despite similar species-specific birth weights. We conclude that while dairy sheep and goats can effectively manage high dietary Ca intake without overt signs of hypocalcemia or milk fever, there are 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 periparturient dairy ruminants and highlight the need for balanced dietary strategies to optimize health and productivity in both dams and their offspring.