Effects of body weight at first calving and body weight change on subsequent lactation performance

A successful lactation can be affected by body weight (BW) at calving and BW change during early lactation. The objective of the first study was to evaluate the impacts of variables collected from before first lactation, during early lactation, and genomic evaluations that influence first lactation performance. Data was collected from 3,333 first lactation Holstein cows that calved between January 2021 and December 2022 from one commercial dairy farm. BW at first calving was quartiled; low (Q1), low-mid (Q2), mid-high (Q3), and high (Q4) for BW at the onset of lactation. A multiple linear regression analysis using forward selection was conducted to identify significant predictors of 305 d milk yield. The predictive analysis revealed a positive relationship between milk production and delayed days until conception in first lactation. There were significant differences in ADG between the four BW quartiles, ADG increased as BW at calving increased. BW at calving quartile significantly impacted milk production, with each quartile producing more milk as BW at calving increased. A Kaplan Meier analysis showed that Q1 and Q3 cows were more efficient at becoming pregnant in the 5 to 8 wk following the farm’s voluntary waiting period, but by 200 DIM there was no differences in the probability of pregnancy across the four BW quartiles. Cows in Q3 were predicted to have the greatest body size composite, and cows in Q4 were predicted to be the smallest. There were no differences between predicted body size composite for Q1 and Q2 cows. A higher BW at calving and increased d until conception within the first lactation increased milk production. The second study had two objectives, to compare muscle and backfat tissue reserves between primiparous and multiparous dairy cows and examine the relationship between BW loss and muscle and backfat mobilization and milk production in early lactation. Independent of parity, cows were assigned to BW loss group based on percent of total BW loss from 3 to 31 DIM, either low BW loss (LBWL; <6.0%) or high BW loss (HBWL; >6.0%). Milk and blood samples, BW, body condition score (BCS), and ultrasound measurements were taken on 3, 10, 17, 24, and 31 DIM. Milk yield was recorded, and samples were taken from each milking of each sampling day. Blood samples were taken to measure glucose, beta-hydroxybutyrate (BHB), plasma insulin, 3-methylhistidine and creatinine concentrations. Three ultrasound images above the 12th intercostal space of the longissimus dorsi were collected to quantify muscle and backfat depth and change from 3 to 31 DIM. Multiparous cows had greater milk yield, milk protein, and milk fat compared with primiparous cows; however, BW loss did not affect milk production variables. Primiparous cows had higher blood glucose concentrations and greater loss in backfat depth. Regardless of parity, muscle depth decreased as DIM increased. There was no effect of parity on muscle depth in early lactation with cows having similar muscle reserves, regardless of parity. Additionally, weekly BW measurements to assess BW change in early lactation were not indicative of muscle or backfat mobilization in early lactation.