Short communication: Feed utilization and its associations with fertility and productive life in 11 commercial Pennsylvania tie-stall herds.

The objectives of this study were to quantify the relationships of various definitions of feed utilization with both fertility and productive life. Intake and body measurement data were collected monthly on 970 cows in 11 tie-stall herds for 6 consecutive months. Measures of feed utilization for this study were dry matter intake (DMI), dry matter intake efficiency (DME, defined as 305-d fat-corrected milk/305-d DMI), DME with intake adjusted for maintenance requirements (DMEM), crude protein efficiency (defined as 305-d protein yield/305-d crude protein intake), and 2 definitions of residual feed intake (RFI). The first, RFI(reg), was calculated by regressing daily DMI on daily milk, fat, and protein yields, body weight (BW), daily body condition score (BCS) gain or loss, the interaction between BW and BCS gain or loss, and days in milk. The second, RFI(NRC), was estimated by subtracting 305-d DMI predicted according to their fat-corrected milk and BW from actual 305-d DMI. Data were analyzed with 8-trait animal models and included one measure of feed utilization and milk, fat, and protein yields, BW, BCS, days open (DO), and productive life (PL). The genetic correlation between DME and DO was 0.53 (± 0.19) and that between DME and PL was 0.66 (± 0.10). These results show that cows who had higher feed efficiency had greater DO (undesirable) and greater PL (desirable). Results were similar for the genetic correlation between DO and crude protein efficiency (0.42). Productive life had genetic correlations of -0.22 with BW and -0.48 with BCS, suggesting that larger, fatter cows in this study had shorter PL. Correlations between estimated breeding values for feed utilization and official sire genetic evaluations for fertility were in agreement with the results from the multiple-trait models. Selection programs intended to enhance feed efficiency should factor relationships with functional traits to avoid unfavorable effects on cow fertility.

Heritability of gross feed efficiency and associations with yield, intake, residual intake, body weight, and body condition score in 11 commercial Pennsylvania tie stalls.

The objectives of this study were to calculate the heritability of feed efficiency and residual feed intake, and examine the relationships between feed efficiency and other traits of productive and economic importance. Intake and body measurement data were collected monthly on 970 cows in 11 tie-stall herds for 6 consecutive mo. Measures of efficiency for this study were: dry matter intake efficiency (DMIE), defined as 305-d fat-corrected milk (FCM)/305-d DMI, net energy for lactation efficiency (NELE), defined as 305-d FCM/05-d NEL intake, and crude protein efficiency (CPE), defined as 305-d true protein yield/305-d CP intake. Residual feed intake (RFI) was calculated by regressing daily DMI on daily milk, fat, and protein yields, body weight (BW), daily body condition score (BCS) gain or loss, the interaction between BW and BCS gain or loss, and days in milk (DIM). Data were analyzed with 3- and 4-trait animal models and included 305-d FCM or protein yield, DM, NEL, or CP intake, BW, BCS, BCS change between DIM 1 and 60, milk urea nitrogen, somatic cell score, RFI, or an alternative efficiency measure. Data were analyzed with and without significant covariates for BCS and BCS change between DIM 1 and 60. The average DMIE, NELE, and CPE were 1.61, 0.98, and 0.32, respectively. Heritability of gross feed efficiency was 0.14 for DMIE, 0.18 for NELE, and 0.21 for CPE, and heritability of RFI was 0.01. Body weight and BCS had high and negative correlations with the efficiency traits (-0.64 to -0.70), indicating that larger and fatter cows were less feed efficient than smaller and thinner cows. When BCS covariates were included in the model, cows identified as being highly efficient produced 2.3 kg/d less FCM in early lactation due to less early lactation loss of BCS. Results from this study suggest that selection for higher yield and lower BW will increase feed efficiency, and that body tissue mobilization should be considered.

Genetic parameters of feed intake, production, body weight, body condition score, and selected type traits of Holstein cows in commercial tie-stall barns.

The objectives of this study were to determine the feasibility of measuring feed intake in commercial tie-stall dairies and infer genetic parameters of feed intake, yield, somatic cell score, milk urea nitrogen, body weight (BW), body condition score (BCS), and linear type traits of Holstein cows. Feed intake, BW, and BCS were measured on 970 cows in 11 Pennsylvania tie-stall herds. Historical test-day data from these cows and 739 herdmates who were contemporaries during earlier lactations were also included. Feed intake was measured by researchers once per month over a 24-h period within 7 d of 6 consecutive Dairy Herd Information test days. Feed samples from each farm were collected monthly on the same day that feed intake was measured and were used to calculate intakes of dry matter, crude protein, and net energy of lactation. Test-day records were analyzed with multiple-trait animal models, and 305-d fat-corrected milk yield, dry matter intake, crude protein intake, net energy of lactation intake, average BW, and average BCS were derived from the test-day models. The 305-d traits were also analyzed with multiple-trait animal models that included a prediction of 40-wk dry matter intake derived from National Research Council equations. Heritability estimates for 305-d intake of dry matter, crude protein, and net energy of lactation ranged from 0.15 to 0.18. Genetic correlations of predicted dry matter intake with 305-d dry matter, crude protein, and net energy of lactation intake were 0.84, 0.90, and 0.94, respectively. Genetic correlations among the 3 intake traits and fat-corrected milk yield, BW, and stature were moderate to high (0.52 to 0.63). Results indicate that feed intake measured in commercial tie-stalls once per month has sufficient accuracy to enable genetic research. High-producing and larger cows were genetically inclined to have higher feed intake. The genetic correlation between observed and predicted intakes was less than unity, indicating potential variation in feed efficiency.

Heritability estimates associated with alternative definitions of mastitis and correlations with somatic cell score and yield.

The objectives of this study were to compare alternative mastitis definitions and to estimate genetic correlations of producer-recorded mastitis with somatic cell score (SCS) and yield. Cow health events and lactation records from June 2002 through October 2007 were provided by Dairy Records Management Systems (Raleigh, NC). First- through fifth-lactation records from cows calving between 20 and 120 mo of age and that calved in a herd-year with at least 1% of cows with a clinical mastitis event were retained. The edited data contained 118,516 lactation records and 1,072,741 test-day records of 64,893 cows. Mastitis occurrence (1 = at least one mastitis event during lactation or test-day interval, 0 = no mastitis events), number of mastitis events during lactation, SCS, and yield were analyzed with animal models (single trait) or sire-maternal grandsire models (multiple trait) in ASREML. Comparisons were made among models assuming a normal distribution, a binary distribution, or Poisson distribution (for total episodes). The overall incidence of clinical mastitis was 15.4%; and heritability estimates ranged from 0.73% (test-day interval mastitis with a linear model) to 11.07% (number of mastitis episodes with a Poisson model). Increased mastitis incidence was genetically correlated with higher SCS (range 0.66 to 0.88) and was generally correlated with higher yield (range -0.03 to 0.40), particularly during first lactation (0.04 to 0.40). Significant genetic variation exists for clinical mastitis; and health events recorded by producers could be used to generate genetic evaluations for cow health. Sires ranked similarly for daughter mastitis susceptibility regardless of how mastitis was defined; however, test-day interval mastitis and a total count of mastitis episodes per lactation allow a higher proportion of mastitis treatments to be included in the genetic analysis.

Milk urea nitrogen concentration: heritability and genetic correlations with reproductive performance and disease.

The objectives of this study were to estimate the heritability of milk urea nitrogen (MUN) concentration and describe the genetic relationship between MUN and reproductive performance and between MUN and diseases in Holsteins. Dairy Records Management Systems (Raleigh, NC) provided lactation data. The Danish Agricultural Advisory Center provided breeding value estimates for diseases. Infrared (IR) and wet chemistry (WC) data were analyzed separately. Heritabilities and genetic correlations for 2 different measures of MUN and reproductive performance were estimated with an animal model using ASREML. Heritabilities for MUN were estimated using all lactations combined (lactations 1 through 5) and separately for first lactation and second lactation. Genetic correlations with reproduction and health were estimated separately for parities 1 and 2. Herd-test-day or herd-year-season along with age at calving and days in milk were included as fixed effects in all models. Heritability estimates for all lactations combined were 0.15 for WC MUN and 0.22 for IR MUN. Genetic correlations between WC MUN and 2 measures of reproductive performance, days to first service, and first service conception were not different from zero. In contrast, the genetic correlation between WC MUN and days open of 0.21 in first lactation and 0.41 in second lactation indicated that higher WC MUN values were associated with increased days open. Correlations among estimated breeding values for MUN and estimated breeding values for Danish diseases identified no significant relationships. Although the results of this study indicate that heritable variation for MUN exists, the inability to identify significant genetic relationships with several measures of disease or reproductive performance appears to limit the value of MUN in selection for disease resistance and improved reproduction.

Effects of replacing dietary starch with sucrose on ruminal fermentation and nitrogen metabolism in continuous culture.

A dual-effluent continuous-culture system was used to evaluate the effects of partially replacing cornstarch with sucrose in a total mixed ration on ruminal fermentation and N metabolism. The 4 treatments were 0 (control), 2.5, 5.0, and 7.5% sucrose and, respectively, 7.5 (control), 5.0, 2.5, and 0% cornstarch in a total mixed ration containing 20% corn silage and 40% alfalfa silage. Fermenters were fed 4 times a day during four 9-d periods with sampling beginning on d 6. Replacing cornstarch with sucrose did not alter ruminal pH (5.97), total volatile fatty acids (VFA) (104.4 mmol/L), or the acetate to propionate ratio (2.16); however, branched-chain volatile fatty acids were higher for the control treatment compared with the 7.5% sucrose treatment. Five hours postfeeding, sucrose treatments significantly altered molar proportions of all volatile fatty acids, and acetate-to-propionate and glucogenic-to-lipogenic ratios. Digestibility of dry matter and N were not affected by treatment, but digestibility of total non-structural carbohydrates was increased with sucrose treatments. A quadratic effect was noted for neutral detergent fiber (NDF) digestibility as sucrose replaced starch. A higher NDF digestibility (66.1 vs. 59.9%) was observed for the 7.5% sucrose treatment compared with the other 2 sucrose treatments. Levels of ammonia N were within an acceptable range to support microbial protein synthesis and did not differ among treatments (mean=9.23 mg/dL). Sucrose inclusion in the total mixed ration did not affect bacterial N synthesis. Results indicate that (at the levels tested in this study) inclusion of sucrose in the diet when rumen-degradable protein is adequate does not affect ruminal fermentation.

Effects of prepartum somatotropin and monensin on metabolism and production of periparturient Holstein dairy cows.

Fifty-five multiparous Holstein dairy cows were used to evaluate the singular and combined effects of somatotropin and monensin treatments during the late dry period on postpartum metabolism and production. Treatments were 1) control (C); 2) injection of exogenous bovine somatotropin (bST); 3) TMR top dressed with 300 mg of monensin/day (M); and 4) monensin and somatotropin in combination (bST+M) during the last 28 days before expected parturition. A 500-mg subcutaneous injection of sustained release somatotropin was administered adjacent to the tail head at d -28 and -14 relative to expected calving. Diet and management were the same for all cows after parturition. Production and intake were measured daily until 63 d in milk. Milk composition, blood metabolites, and body weight and condition score were measured weekly. Prepartum glucose, nonesterified fatty acid, and blood urea nitrogen concentrations were not different among treatments. Cows on the M treatment tended to have greater dry matter intake postpartum than those on the C treatment and 30% lower plasma nonesterified fatty acid concentrations during wk 1 postpartum than all other treatments. Milk yield and milk fat yield were not different among treatments, but milk fat percent tended to be lower for the bST+M treatment than the C treatment. Changes in plasma amino acid concentrations were consistent with mobilization of skeletal muscle protein, possibly for use in gluconeogenesis. Results from this study provide evidence that prepartum feeding of monensin reduced plasma nonesterified fatty acid concentrations and may improve glucose metabolism of the periparturient dairy cow.

Monensin and growth hormone effects on glucose metabolism in the prepartum cow.

Twenty-seven multiparous Holstein dairy cows were used to evaluate the singular and combined effects of somatotropin and monensin treatments during the late dry period on postpartum metabolism and production. Treatments were 1) control, 2) injection of exogenous bovine somatotropin (bST); 3) total mixed rations top-dressed with 300 mg of monensin/d, and 4) monensin and somatotropin in combination, during the last 28 d before expected parturition. A 500-mg subcutaneous injection of sustained-release somatotropin was administered at d-28 and -14 relative to expected calving. Glucose kinetics was evaluated on d 15 before expected calving date using a tracer dose of 45 mg of U-13C-labeled glucose. Jugular blood was sampled 20 times during 8 h after tracer injection. Intake of DM was 1.9% of BW, and daily feed was supplied in six equal meals before the glucose kinetic assay. The CONSAM simulation program, which assumes a two-compartment model, was used to analyze the glucose 13C enrichment curves with time. Average glucose distribution space, glucose mass, and glucose residence time in compartment 1 were increased in monensin-treated cows and were decreased in bST-treated cows. On the day of the glucose kinetic assay, blood concentrations of glucose, NEFA, and urea were similar among treatments. The changes in glucose pool and distribution space suggest that monensin increases propionate supply and bST facilitates glucose flow into glucose consuming organs. It is concluded that dairy cows might benefit from a combined application of monensin and bST before parturition.