Does ß-hydroxybutyrate concentration influence conception date in young postpartum range beef cows?

Cows in negative energy balance after calving often have reduced reproductive performance, which is mediated by metabolic signals. The objective of these studies was to determine the association of serum metabolites, days to first postpartum ovulation, milk production, cow BW change, BCS, and calf performance with conception date in spring-calving 2- and 3-yr-old beef cows grazing native range. In Exp. 1, cows were classified by conception date in a 60-d breeding season as early (EARLY; conceived in first 15 d of breeding) or late conception (LATE; conceived during the last 45 d of breeding). Beginning on d 35 postpartum, blood samples were collected twice per week for serum metabolite analysis and progesterone analysis to estimate days to resumption of estrous cycles. As a chute-side measure of nutrient status and glucose sufficiency, whole-blood ß-hydroxybutyrate (BHB) concentrations were measured 14 ± 2 d before breeding. In Exp. 2, cows were classified by subsequent calving date resulting from a 55 ± 2 d breeding season as conceiving either early (EARLY; conceived in first 15 d of breeding) or late (LATE; conceived during the remaining breeding season). Blood samples were collected in 2 periods, 30 ± 4 d before calving and 14 ± 3 d before the initiation of breeding, to determine circulating concentrations of IGF-I and BHB. In Exp. 1, BHB and serum glucose concentrations were less (P ≤ 0.04) in EARLY cows than LATE cows. Serum insulin concentrations were greater (P = 0.03) in EARLY cows relative to LATE cows. Milk production and composition did not differ (P ≥ 0.24) by conception date groups. In Exp. 2, cow age × sample period × conception date interaction (P < 0.01) occurred for serum BHB concentrations. Serum BHB concentrations were similar (P > 0.10) for 2-yr-old cows (in greater nutritional plane compared with Exp. 1) regardless of their conception date classification and sampling period. However, precalving serum BHB concentrations were greater (P < 0.01) for LATE than EARLY in 3-yr-old cows with no difference (P = 0.86) at prebreeding. Serum IGF-1 concentrations were greater (P < 0.01) for EARLY cows relative to LATE cows at precalving and prebreeding. This study indicates that blood BHB concentrations during times of metabolic dysfunctions may provide a more sensitive indicator of energy status than body condition, predicting rebreeding competence in young beef cows as measured by interval from calving to conception.

Relationship between body condition score at calving and reproductive performance in young postpartum cows grazing native range.

Body condition score is used as a management tool to predict competency of reproduction in beef cows. Therefore, a retrospective study was performed to evaluate association of BCS at calving with subsequent pregnancy rate, days to first postpartum ovulation, nutrient status (assessed by blood metabolites), and calf BW change in 2- and 3-yr-old cows (n = 351) managed and selected to fit their environment of grazing native range over 6 yr at the Corona Range and Livestock Research Center, Corona, NM. Cows were managed similarly before calving, without manipulation of management, to achieve predetermined BCS at parturition. Palpable BCS (scale of 1 to 9) were determined by 2 experienced technicians before calving. Cows were classified to 1 of 3 BCS groups prior calving: BCS 4 (mean BCS = 4.3 ± 0.02), 5 (mean BCS = 5.0 ± 0.03), or 6 (mean BCS = 5.8 ± 0.06). Cows were weighed weekly after calving and serum was collected once weekly (1 yr) or twice weekly (5 yr) for progesterone analysis to estimate first postpartum ovulation beginning 35 d postpartum. Year effects also were evaluated, with years identified as either above or below average precipitation. Days to first postpartum ovulation did not differ among calving BCS groups (P = 0.93). Pregnancy rates were not influenced by calving BCS (P = 0.83; 92%, 91%, 90% for BCS 4, 5, and 6, respectively). Days to BW nadir was not influenced by BCS at calving (P = 0.95). Cow BW was different at all measuring points (P < 0.01) with BCS 6 cows having the heaviest BW and cows with BCS 4 the lightest. Cows with calving BCS 4 and 5 lost more (P = 0.06) BW from the initiation of the study to the end of breeding than cows with BCS 6. However, cow BW change at all other measurement periods was not different (P ≥ 0.49) among calving BCS groups. Serum glucose and NEFA concentrations were not influenced by calving BCS (P ≥ 0.51). Calf BW at birth (P = 0.60), branding (55-d BW; P = 0.76), and weaning (205-d BW; P = 0.60) were not impacted by cow calving BCS. Body condition score did not influence overall pregnancy rates, indicating that young cows can have a reduced BCS and still be reproductively punctual. Therefore, these results indicate that reproductive performance of young cows with reduced BCS may not be affected when managed in extensive range conditions.

The effect of increasing amount of glucogenic precursors on reproductive performance in young postpartum range cows.

Supplementing CP and propionate salts (PS) may improve economic returns in young range beef cows by increasing the dietary supply of glucogenic precursors. A 3-yr study conducted at Corona Range and Livestock Research Center (Corona, NM) from February to mid-July in 2005 (n = 80), 2006 (n = 81), and 2007 (n = 80) evaluated days to first estrus, calf weaning weight, BW change, and metabolic responses in 2- and 3-yr-old postpartum cows grazing native range. Cows were individually fed one of three 36% CP supplement treatments after parturition, with increasing glucogenic potential (GP) supplied by RUP and PS. Supplements were isoenergetic and fed at a rate of 908 g/cow per day twice weekly. Supplementation was initiated 7 d after calving and continued for an average of 95 d. Supplement treatments provided 1) 328 g of CP, 110 g of RUP and 0 g of PS (PS0); 2) 328 g of CP, 157 g of RUP, and 40 g of PS (PS40); or 3) 329 g of CP, 158 g of RUP, and 80 g of PS (PS80). Ultimately, PS0, PS40, and PS80 provided 44, 93, and 124 g of GP, respectively. Body weight was recorded weekly and serum was collected twice weekly for progesterone analysis to estimate days to first estrus. Cows were exposed to bulls for 60 d or less beginning in mid-May. Days to first estrus exhibited a quadratic (P = 0.06) response to GP resulting from the fewest days to first estrus with the consumption of PS40. Pregnancy rates were 88, 96, and 94% for cows fed PS0, PS40, and PS80, respectively (P = 0.11). Total kilograms of calf weaned per cow exposed to bulls for the supplementation and following year increased quadratically (P = 0.09). However, supplement did not affect milk composition or yield (P ≥ 0.53). Serum acetate half-life decreased linearly (P = 0.08) with increasing GP in 2007. Predicted margins were the greatest (quadratic; P = 0.03) for cows fed PS40. Even though supplement costs were greater for PS40 and PS80, cows fed PS40 had increased profits ($33.47/cow) compared with cows fed PS0 and PS80. This study implies that young postpartum cows fed additional glucogenic precursors may have improved reproductive efficiency and may wean more calf weight per cow exposed to breeding.

Protein and glucogenic precursor supplementation: a nutritional strategy to increase reproductive and economic output.

Reproductive performance in young beef cows is often compromised due to a mismatch of physiological demands and suboptimal environmental conditions. Studies conducted at the Corona Range and Livestock Research Center from 2000 to 2007 evaluated 3 postpartum supplement strategies that varied in the amount of glucogenic potential (GP) supplied. Reproductive variables, milk production, and serum metabolites were used to assess supplement effectiveness and economics associated with 2- and 3-yr-old beef cows (n = 379) grazing native range. Supplements were individually fed twice/week at 1,135 g/d (2003 to 2004) or 908 g/d (all other years) and provided 1) 327 g of CP, 109 to 118 g of RUP (CON); 2) 327 to 341 g of CP, 142 to 157 g of RUP (RUP); or 3) 327 g of CP, 151 to 173 g of RUP + 40 to 100 g of propionate salt (PS; RUP+PS). Ultimately, total GP for CON, RUP, and RUP+PS was 44 to 47, 57 to 70, and 93 to 141 g, respectively. Blood samples were collected once/week (2000) or twice/week (2001 to 2007) for progesterone analysis to estimate days to resumption of estrus. Cows were exposed to bulls for 60 d or less, and pregnancy was confirmed by rectal palpation at weaning. Days to resumption of estrus after calving decreased linearly (P = 0.02), resulting in an increased pregnancy rate (P = 0.03) with increasing GP. Milk production exhibited a quadratic (P = 0.04) response to increasing GP, with cows fed RUP producing the most amount of milk. However, a linear decrease (P = 0.07) in days from BW nadir to estrus was found with increasing GP. Total kilograms of calf weaned per cow exposed for the supplemental year and subsequent year was increased linearly (P = 0.07) with increased GP. The improvement in pregnancy rate by supplementing RUP+PS resulted in an increase in total revenue of 18% compared with CON-fed cows and 9.5% compared with RUP-fed cows in the subsequent year after supplementation. These data suggest feeding young cows additional GP in the form of PS allows for partitioning of nutrients away from milk production and toward reproduction, allowing for increased profitability by increasing pregnancy rates and decreasing days to resumption of estrus.

The major histocompatibility complex and autoimmunity.

Study of two diseases with autoimmune characteristics (IDDM and SLE) has demonstrated that alleles carried in the MHC can confer disease susceptibility. The MHC alleles most strongly associated with the development of IDDM are encoded within the class II region (HLA-DR or -DQ). Recent studies indicating that the class III gene products TNF alpha and beta may play a critical role in the initiation of the autoimmune attack on the pancreatic beta-cells have suggested the possibility that the class III region may also contribute to genetic susceptibility in IDDM. In SLE, although there is some evidence suggesting that certain alleles of class II genes may confer disease risk, a more striking association has been detected in the class III region. Deficiency of the class III encoded C4A molecule (either homozygously or heterozygously) shows a high correlation with disease risk. This finding is attractive because C4A plays a central role in the metabolism of immune complexes, the aberrant deposition of which leads to the most prominent alterations in SLE.

Deletion of C4A genes in patients with systemic lupus erythematosus.

To define the relationship between inheritance of major histocompatibility complex (MHC) alleles and susceptibility to the development of systemic lupus erythematosus (SLE), we examined the MHC class I, II, and III phenotypes of white SLE patients and characterized the structures of their class III MHC genes, using Southern blotting. Nine of 88 SLE patients (10.2%) were C4A null. As detected by Southern blot analysis, the C4A gene was deleted from both chromosomes in 8 of the 9 C4A-null patients. Deletions affecting only 1 chromosome (heterozygous) were detected in the remaining C4A-null patient and in 34.5% of SLE patients who were not C4A deficient (compared with 12.5% of controls; P less than 0.05). These results indicate that deletion of the C4A gene is a common genetic marker for SLE. Deletions of C4A were observed most commonly as part of the HLA-B8;DR3 extended haplotype, although deletions were also detected in different HLA haplotypes. Because of the critical role of C4A in the processing of immune complexes, deficiency of C4A may, itself, confer susceptibility to the development of SLE.