Effect of level of dietary cation anion difference and duration of prepartum feeding on calcium and energy metabolism in transition cows

• Grant number: 15/22047-4
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Effective date (Start): December 31, 2015
• Effective date (End): March 04, 2016
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Animal Reproduction
• Principal Investigator: Claudia Maria Bertan Membrive
• Grantee: Barbara Piffero Mello
• Supervisor: José Eduardo P. Santos
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Research place: University of Florida, Gainesville (UF), United States
• Associated to the scholarship: 15/03331-3 - Study the mechanisms of action by which estradiol stimulates endometrial PGF2a synthesis in cows: assessment of its effects on the population of endometrial receptors for progesterone and estradiol, BP.IC

Abstract

The calcium status is important to activate immunological cells (Lewis, 2001) therefore it affects the risk of uterine diseases in dairy cows (Martinez, 2012) and these diseases delay post-partum ovulation, decrease pregnancy rates by artificial insemination (AI) and increase pregnancy loss. Manipulating the mineral composition of the prepartum ration by incorporating acidogenic salts to reduce the dietary cation-anion difference (DCAD) induces a compensated metabolic acidosis and improves calcium (Ca) metabolism at the onset of lactation, which prevents milk fever. The efficacy of negative DCAD rations to prevent milk fever is well documented (Ender et al., 1971; Block, 1984). Nevertheless, major concerns exist when cows are fed acidogenic salts in excess that induce a more exacerbated metabolic acidosis (Bigner et al., 1996). The objective of this study is to determine the effects of extending the feeding of acidogenic salts prepartum at two levels of negative DCAD on energy and mineral metabolism, production, and health in dairy cows. The study will be conducted in the University of Florida, Gainesville (USA). It will be used 72 late gestation parous Holstein cows, at 235 days of gestation (approximately 6 weeks prepartum) will be blocked by lactation and randomly assigned to one of four treatments arranged as 2 x 2 factorial. The main effects of treatments are level of negative DCAD (-80 mEq/kg vs. -200 mEq/kg) and duration of feeding prepartum (3 vs. 6 weeks). The equation used to calculate the DCAD will be: [(mEq of K + mEq of Na) - (mEq of Cl + mEq of S)] (Block, 1984; Charbonneau et al., 2006). Prepartum and postpartum cows will be housed in free stall barns equipped with individual feeding gates. Cows will be moved to the research facility at 235 days of gestation. The changes in DCAD will be imposed by increasing the amount of acidogenic salt high in chloride (Cl) to create the -80 and -200 mEq/kg. Diets will be isocaloric and isonitrogenous, and contain the same amount of forage and fiber. Every attempt will be made to vary only Cl in the diets. Cows in the short duration of DCAD feeding (3 weeks) will receive the same diet, but without any acidogenic salts from 235 to 255 days of gestation, after which they will receive either the -80 or -200 mEq/kg DCAD diet. Cows in the long duration of feeding (6 weeks) will start the experiment receiving one of the two negative DCAD diets. During the experiment will be measured DM intake, milk production and composition, body weight, body condition score and health, urinary pH and excretion of Ca, magnesium and phosphorus, will be taken blood sampling to analyses Ca, magnesium, phosphorus, NEFA, BHBA, glucose and insulin and finally will be made an insulin challenge and glucose tolerance test. (AU)