Abstract
Restricted dietary P supply to transition dairy cows has recently been reported to beneficially affect the Ca balance of periparturient cows. The objective of the present study was to determine whether this effect on the Ca balance can be reproduced when limiting the P-restricted feeding to the last 4 wk of gestation. A total of 30 dairy cows in late pregnancy were randomly assigned to a dry cow diet with either low or adequate P content (0.16 and 0.30% P in DM, respectively) to be fed in the 4 wk before expected calving. After calving, all cows received the same lactating cow ration with adequate P content (0.46% P in DM). Blood was collected daily from 4 d antepartum until calving, at calving (d 0), 6 and 12 h after calving (d +0.25 and d +0.5, respectively) and on days +1, +2, +3, +4 and +7 relative to calving. Blood gas analyses were conducted to determine the concentration of ionized Ca in whole blood ([Ca2+]), and plasma was assayed for concentrations of inorganic phosphorus ([Pi]), total calcium, parathyroid hormone ([PTH]), 1,25-dihydroxyvitamin D ([1,25-(OH)2D3]), and CrossLaps ([CTX]), a biomarker for bone resorption (Immunodiagnostic Systems GmbH). Repeated-measures ANOVA was conducted to study treatment, time, and lactation number effects. The mean [Ca2+] in P-deprived cows remained above the threshold of 1.10 mmol/L throughout the study, and values were higher compared with cows on adequate P supply between d 0 and d +2 and on d +4. The [Ca2+] differed between treatments at the sampling times d 0, d +0.25, d +0.5, d +2, and d +4. Plasma [PTH] and [1,25-(OH)2D3] did not differ between treatments, but P-deprived cows had greater [CTX] than cows with adequate P supply at d +1, d +2, and d +7. These results indicate that restricted dietary P supply to during the last 4 wk of the dry period improves the Ca homeostasis of these cows in the first days of lactation, an effect that seems to be primarily driven by increased bone tissue mobilization.
Highlights
Periparturient hypocalcemia is recognized as one of the most important metabolic disturbances of the dairy cow in early lactation (USDA, 2002)
Of the 30 cows included in the study, 7 and 8 cows assigned to the adequate P content (AP) and low P (LP) treatments, respectively, entered the second lactation, 5 and 4 cows entered the third lactation, and 3 cows of each treatment entered the fourth lactation
The objective of this study was to determine whether a feeding protocol restricting the dietary P supply during the last 4 wk of the dry period was effective in improving the Ca homeostasis of high-yielding periparturient dairy cows
Summary
Periparturient hypocalcemia is recognized as one of the most important metabolic disturbances of the dairy cow in early lactation (USDA, 2002). Most milk fever prevention strategies currently in use in the dairy industry aim at enhancing bone mobilization and intestinal Ca absorption through stimulation of the secretion of parathyroid hormone (PTH) and Wächter et al.: RESTRICTED PHOSPHORUS AND HYPOCALCEMIA increasing tissue responsiveness to PTH. Approaches based on this concept include, among others, feeding Ca-deficient or low-DCAD diets during the close-up dry period, and the use of Ca binders. The aforementioned study applied dietary P restriction throughout the transition period extending to 4 wk postpartum, which was associated with decreased DMI and milk production in early lactation in P-deprived cows. The ensuing question that remained unresolved far is whether limiting dietary P restriction strictly to the dry period would achieve the same positive effect on the Ca balance during the fresh cow period as described by Cohrs et al (2018) under prolonged dietary P deprivation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
