The preweaning management of dairy calves over the last 30 yr has focused on mortality, early weaning, and rumen development. Recent studies suggest that nutrient intake from milk or milk replacer during the preweaning period alters the phenotypic expression for milk yield. The objective of this study was to investigate the relationship between nutrient intake from milk replacer and pre- and postweaning growth rate with lactation performance in the Cornell dairy herd and a commercial dairy farm. The analysis was conducted using traditional 305-d first-lactation milk yield and residual lactation yield estimates from a test-day model (TDM) to analyze the lactation records over multiple lactations. The overall objective of the calf nutrition program in both herds was to double the birth weight of calves by weaning through increased milk replacer and starter intake. First-lactation 305-d milk yield and residuals from the TDM were generated from 1,244 and 624 heifers from the Cornell herd and from the commercial farm, respectively. The TDM was used to generate lactation residuals after accounting for the effects of test day, calving season, days in milk, days pregnant, lactation number, and year. In addition, lactation residuals were generated for cattle with multiple lactations to determine if the effect of preweaning nutrition could be associated with lifetime milk yield. Factors such as preweaning average daily gain (ADG), energy intake from milk replacer as a multiple of maintenance, and other growth outcomes and management variables were regressed on TDM milk yield data. In the Cornell herd, preweaning ADG, ranged from 0.10 to 1.58 kg, and was significantly correlated with first-lactation yield; for every 1 kg of preweaning ADG, heifers, on average, produced 850 kg more milk during their first lactation and 235 kg more milk for every Mcal of metabolizable energy intake above maintenance. In the commercial herd, for every 1 kg of preweaning ADG, milk yield increased by 1,113 kg in the first lactation and further, every 1 kg of prepubertal ADG was associated with a 3,281 kg increase in first-lactation milk yield. Among the 2 herds, preweaning ADG accounted for 22% of the variation in first-lactation milk yield as analyzed with the TDM. These results indicate that increased growth rate before weaning results in some form of epigenetic programming that is yet to be understood, but has positive effects on lactation milk yield. This analysis identifies nutrition and management of the preweaned calf as major environmental factors influencing the expression of the genetic capacity of the animal for milk yield.

Energy balance and serum progesterone concentrations were monitored during early lactation in a group of high producing Holstein cows. The postpartum interval to normal ovulation averaged 36 +/- 6 days (range 6 to 83 days). Average energy balance during the first 20 days of lactation (cumulative daily calculated energy balance divided by days in milk) was inversely related to days to normal ovulation (r = -.60) and to milk production (r = -.80). Milk yield during this period was not closely related to days to ovulation (r = .30). Milk yield was also not significantly related to serum prolactin concentrations over the first 12 weeks of lactation (r = .27). During early lactation, energy balance was maximally negative until peak milk yield and then began returning toward zero, with the magnitude and duration of negative energy balance being quite variable. On the average, ovulation and the initiation of the first normal luteal phase occurred approximately 10 days after energy balance began returning toward zero. During this 10-day interval, a transient elevation in serum progesterone concentrations occurred in eight of 13 cows. These results suggest that energy balance during the first 20 days of lactation is important in determining the onset of ovarian activity following parturition.

The effects of body weight (BW) gain, different sources of protein during the prepubertal period (90 to 320 kg of BW), and the performance of Holstein heifers during their first lactation were studied. Heifers (n = 273) were assigned to one of three dietary energy treatments that were designed to achieve average daily gains of 0.6, 0.8, and 1.0 kg/d. Within each energy treatment, different protein sources (plant protein and urea or both plant and animal proteins) were imposed. Actual average daily gains by heifers on each energy treatment were 0.68, 0.83, and 0.94 kg/d for heifers that were fed diets formulated for average daily gains of 0.6, 0.8, and 1.0 kg/d, respectively, which allowed the following ages at first calving: 24.5, 22.0, and 21.3 mo. Breeding was initiated when heifers weighed approximately 340 kg. Protein sources did not affect average daily gain or milk yield. Analysis of the preplanned comparisons of actual 305-d and 4% fat-corrected milk yields indicated that yield was significantly reduced for heifers grown at 0.94 kg/d (9387 and 8558 kg, respectively) compared with that of heifers grown at 0.68 kg/d (9873 and 9008 kg, respectively). However, further regression analysis of fat-corrected milk and residual milk from a test day model on prepubertal BW gain only explained 8 and 2% of the variation in milk yield, respectively. Postcalving BW and body condition score were different among treatments. Posttreatment factors, such as postcalving BW, accounted for more of the variation in milk yield than did prepubertal BW gain. Prepubertal BW gains, when evaluated on a continuum from 0.5 to 1.1 kg/d, explained little of the variation in milk yield; therefore, BW gain during the prepubertal period did not significantly affect milk yield during first lactation.

No abstract

Responses of registered Holstein cows to various levels of inbreeding were examined with pedigree data supplied by the Holstein Association USA and test-day production data from 1970 through 1998 obtained from the Animal Breeding Center at Cornell University. Rate of increase in level of inbreeding has been accelerating over time, making it more difficult for producers to make matings that avoid the potentially deleterious effects of inbreeding. Milk production losses per lactation caused by inbreeding were generally 35 kg per percentage inbreeding level >0.01 but increased to 55 kg per percentage inbreeding level from 0.07 to 0.10. Somatic cell score was not affected by level of inbreeding. Inbreeding had the greatest effect on production at ages <22 mo and early in lactation. Early onset of the deleterious effects of inbreeding resulted in larger net present value losses than when effects of inbreeding occurred later. Losses were likely enhanced due to the need to freshen animals as early as possible to maximize net present value returns. Survival decreased as level of inbreeding increased and was likely to have a greater negative impact on the financial health of the dairy enterprise than production losses.