Dairy producers and nutrition consultants alike understand the importance of a well-managed nutritional program during the transition period for the health and productivity of their herd. The success, or lack thereof, of these nutrition programs has potential to affect the productivity and longevity of cows and thereby influence farm profitability.
While research findings and on-farm observations have guided adoption of close-up and fresh pens and the formulation of the diets fed to these cows, uncertainty remains around the optimal metabolizable protein (MP) supply to feed during these stages of the lactation cycle.
Amino acids are essential building blocks for protein synthesis and demand increases around the time of calving to support development of the fetus and mammary gland, as well as for synthesis of colostrum and milk. A concurrent reduction in dry matter intake (DMI) exposes cows to a transient, yet prominent, protein deficit that can be further exacerbated by diet composition and might have negative consequences on production efficiency. While increasing the close-up MP supply has generated inconsistent early lactation milk production responses, cows appear to respond to an increased postpartum MP supply with increased milk production. However, it remains unknown whether these positive responses are facilitated by an increased supply of the first-limiting amino acids, methionine and lysine, and if short-term MP supplementation during the transition period has potential to affect performance beyond the feeding period.
To investigate such questions, a randomized block design study was conducted at Cornell University. Multiparous Holstein cows (n = 96) were assigned to one of four dietary treatment groups consisting of a combination of a prepartum and a postpartum diet (Figure 1). At 28 days relative to expected calving, cows were fed a close-up diet formulated to contain either a control (C; 39 g of MP/lb. DM) or high (H; 51 g of MP/lb. DM) level of estimated MP. From calving to 21 days in milk (DIM), diets were formulated to contain either a control (C; 47 g of MP/lb. DM) or high (H; 59 g of MP/lb. DM) level of estimated MP. To control the potential confounding effect of methionine (Met) and lysine (Lys) supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of metabolizable energy (ME) in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and postpartum diet resulted in four treatment groups: 1) CC (n = 23), 2) CH (n = 24), 3) HC (n = 22), and 4) HH (n = 23). A common lactation diet (51 g of MP/lb. DM) was fed from 22 DIM to the end of the observation period at 42 DIM. Diets were formulated using the Cornell Net Carbohydrate and Protein System v. 6.5.5 (CNCPS; AMTS.Cattle.Professional v. 4.17.0.0).
Close-up diets were formulated using conventional corn silage (45.0 percent of DM), wheat straw (26.7 percent of DM) and a grain mix (28.3 percent of DM). Metabolizable protein concentrations were established to meet and exceed the estimated CNCPS MP requirement during the close-up period. Fresh diets were formulated using brown mid-rib corn silage (37.3 percent of DM), haylage (17.8 percent of DM), wheat straw (4.7 percent of DM), corn grain (17.2 percent of DM), and a grain mix (23.0 percent of DM). Metabolizable protein concentrations were established to represent MP concentrations in fresh cow diets fed on commercial farms in the northeast U.S. and to decrease the MP deficit during the fresh period. Metabolizable protein concentration was increased in both the close-up and fresh H diets using heat-treated soybean meal and an animal-based protein supplement. Commercially available rumen-protected methionine and lysine were used to meet targeted values and balance methionine and lysine relative to metabolizable energy in the close-up and fresh diets. Rumen-degradable protein was 7.5 and 9.0 percent of DM for the close-up C and H diets and 9.1 and 8.9 percent of DM for the fresh C and H diets, respectively. Rumen-undegradable protein was 3.7 and 7.1 percent of DM for the close-up C and H diets and 5.0 and 8.3 percent of DM for the fresh C and H diets, respectively.
PREPARTUM PERIOD
During the close-up period, cows fed the H diet consumed 1.1 ± 0.6 lbs. more DM and gained 24.7 ± 7.1 lbs. more bodyweight (BW) than cows fed C, but DMI as a percentage of BW and body condition score (BCS) did not differ by treatment. The resulting MP supply was 1,606 ± 27 and 1,180 ± 27 g/day for cows fed H and C, respectively. At calving, calf birth weight and colostrum yield, quality, and composition, harvested within eight hours of calving, were not affected by prepartum MP supply.
POSTPARTUM PERIOD
Dry matter intake averaged 45.7 ± 0.8 lbs./day from one to 21 DIM and 56.5 ± 1.1 lbs./day from 22 to 42 DIM and were not affected by treatment. The resulting MP supply from one to 21 DIM was greater for cows fed the postpartum H diet (CH: 2766 ± 50; HH: 2667 ± 51 g/day) compared to cows fed the postpartum C diet (CC: 2033 ± 51; HC: 2030 ± 52 g/day). Cows favorably responded to an increased postpartum MP supply by producing greater yields of milk, fat, and protein (Figure 1) during the immediate postpartum period and the increased performance was maintained from 22 to 42 DIM when all cows were fed the same diet. Overall, feeding the H postpartum diet resulted in an increase of 8.6 to 18.5 lbs./day of energy-corrected milk (ECM) from one to 21 DIM and 10.8 to 11.5 lbs./day more ECM from 22 to 42 DIM compared to cows fed the C postpartum diet.
These responses were intriguing as we did not find evidence of treatment differences in body tissue mobilization using visual body condition score (BCS) assessment, circulating indicators of muscle and adipose tissue mobilization, and by determining the backfat thickness and longissimus dorsi muscle diameter using ultrasonography during the immediate postpartum period.
Moreover, we found that cows fed CC lost a greater amount of BW compared to cows fed CH during the first 21 days of lactation, with cows fed HC and HH losing an intermediate amount of BW. While hyperketonemia events did not differ during the first 10 days of lactation, analysis of metabolic indicators revealed that cows fed the H postpartum diet were catabolizing more amino acids and had greater concentrations of ketones in circulation – responses that likely were used to direct sufficient glucose to the mammary gland for milk synthesis.
TAKEAWAYS
When feeding a postpartum MP supply about 2,030 g/day, our data does not support increasing prepartum MP supply greater than 1,200 g/day based on the lack of response in milk yield. However, yields of milk and milk components were increased in response to feeding a high level of MP (about 2,700 g/day) in the fresh diet and the elevated production persisted beyond the initial feeding period. Notably, cows fed a high level of MP during the pre- and postpartum period (HH) produced the most milk and milk components during the first week of lactation, which resulted in a numerically higher ECM (+7.3 ± 2.4 lbs./day) during the first three weeks of lactation when compared to cows fed CH.
These data suggest an opportunity to improve early lactation performance by increasing the MP supply during the postpartum period; and during an appropriate economic situation, producers might benefit from feeding a high level of MP pre- and postpartum.
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This article appeared in PRO-DAIRY's The Manager in November 2024. To learn more about Cornell CALS PRO-DAIRY, visit PRO-DAIRY. |
