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There is no clear method to measure biological efficiency in grazing beef cows. The objective of this study was to evaluate a nutrition model to estimate biological efficiency in mature cows. Data from dams (n = 160) and their 2nd and 3rd progeny were collected from 1953 through 1980. Individual feed intake was measured at 28-d intervals for lifetime of dams and during 240-d lactation for progeny. Body weight of progeny were measured at birth and weaning, and dams at parturition and weaning each production cycle. Milk yield of dams was measured at 14-d intervals by hand milking. Metabolizable energy required (MER) and predicted milk energy yield (MEY) of each cow was computed using the CVDS beef cow model for each parity. Biological efficiency was computed as the ratio of cow ME intake (MEI) to calf weaning weight (WW) based on observed (MEI/WW) and predicted (MER/WW) values. Pearson correlation coefficients were computed using corr.test function in R software. Average (SD) cow weight, calf weaning weight, cow MEI, and observed MEY were 507 (81) and 548 (88) kg, 287 (49) and 294 (44) kg, 9406 (2695) and 9721 (2686) Mcal, and 1009 (538) and 1051 (521) Mcal, for progeny 2 and 3, respectively. Cow MEI and MER (0.87 and 0.85), and observed and predicted MEY (0.51 and 0.51) were positively correlated for progeny 2 and 3, respectively. The CVDS model under predicted cow MEI [mean bias = 1685 (1718) and 1658 (1702) Mcal] and MEY [mean bias = 82 (465) and 129 (450) Mcal] for progeny 2 and 3, respectively. Observed and predicted progeny feed intake were not correlated. Observed and predicted biological efficiency were positively correlated (0.63 and 0.61) for progeny 2 and 3, respectively. In conclusion, nutrition models can reasonably predict biological efficiency, but further refinement of the relationship between calf feed intake and milk yield could improve prediction.

Three sets of blood samples were obtained from beef calves of two experimental populations and assayed for various immunological measurements. The first set of samples was taken between 24 and 48 h after birth and quantified for IgG1 concentration. A second set was taken immediately prior to vaccination for infectious bovine rhinotracheitis virus (IBRV; at an average age of 164 d) and a third set taken 60 d post-vaccination. These later samples were quantified for antibodies specific to IBRV. Level of complement C3 was also quantified in the samples taken immediately prior to vaccination. Three hundred sixty-seven calves were from four Hereford lines; three lines were previously selected for growth traits and the fourth was a randomly selected control line. There were no consistent differences in immune traits among these lines. The second group of 165 animals were Angus, Hereford and Red Poll calves. While Angus calves had a higher mean IgG1 concentration at 24 to 48 h of age than Hereford or Red Poll calves, no differences among breeds were found for the other immune traits measured. Calves from older dams (>3 yr old) tended to have higher mean IgG1 concentrations, pre-vaccination IBRV antibody titers and complement C3 levels than calves from 2- and 3-yr-old cows. However, these calves had lower 60-d post-vaccination IBRV titers than calves from the younger cows (P