Concentrate allowance and corn grain processing influence milk production, body reserves, milk fatty acid profile, and blood metabolites of dairy cows in the early postpartum period

INTRODUCTION:

Immediately after calving, the cow faces the greatest nutritional challenge of the lactation cycle. Optimizing dry matter intake (DMI) during the early postpartum period is critical to providing sufficient energy to support milk production, health, and reproductive performance. Inadequate nutrition during early lactation can negatively impact milk production by 22% to 63% over the following 3 to 12 weeks. Strategies to better meet the nutritional needs of high-producing fresh cows include increasing concentrate levels, raising the concentrate feeding rate, or improving starch digestibility in the rumen and intestine through grain processing techniques.

Increasing concentrate levels generally improves nutrient intake and simultaneously enhances milk production; however, it may not necessarily improve the energy balance. In addition to its impact on production, increasing concentrate levels also affects rumen health, as it has been reported that the rate of concentrate increase after calving influences the fermentation of organic matter (OM) in the rumen, and consequently affects volatile fatty acid (VFA) production and the development of rumen papillae.

Adjusting starch concentration and processing grains can also be used to improve performance and energy balance in cows during early lactation. Enhancing starch digestibility in the rumen and post-rumen through extensive grain processing (e.g., steam flaking) may improve energy utilization and intake efficiency in early-lactation dairy cows. Previous studies have shown that replacing dry ground corn (DGC) with steam-flaked corn (SFC) in fresh dairy cows improved dry matter intake (DMI) and milk production (Zhong et al., 2018; Dhiman et al., 2002). Furthermore, it has been demonstrated that feeding lactating cows SFC instead of dry-rolled corn improved ruminal starch digestibility (52% vs. 35%) and intestinal starch digestibility (93% vs. 61%) (Joy et al., 1997; Crocker et al., 1998). ​

Goals:

Increasing the rate of concentrate feeding may influence energy balance, but few studies have examined the combined effects of a fast (FAS) or slow (SLW) rate of concentrate increase and corn grain processing method (DGC vs. SFC) on the performance of dairy cows in early lactation. Therefore, the objective of this study was to determine the effects of the rate of concentrate increase and corn grain processing method on milk yield and composition, body weight (BW) and body condition score (BCS) changes, and blood metabolites in fresh dairy cows.

MATERIALS AND METHODS:

Forty multiparous Holstein-Friesian cows were randomly assigned to one of four dietary treatments in a 2×2 factorial arrangement within a randomized complete block design (10 cows per treatment). The treatments included two rates of concentrate feeding: fast (FAS) [increasing by 1.0 kg of dry matter (DM) per day] and slow (SLW) [increasing by 0.25 kg DM/day], and two starch sources: dry ground corn (DGC) or steam-flaked corn (SFC). After calving, all cows were fed a basal total mixed ration (TMR) containing 15.8% crude protein (CP) and 19.2% starch on a DM basis (with concentrate composed of 56% grains). During the first 4 days postpartum, all cows received 5 kg of concentrate per day. From day 5 to day 64 postpartum, cows received their assigned treatments. Cows in the FAS group reached 12 kg DM/day of concentrate by day 11, while those in the SLW group reached the same level by day 32. The rations were formulated according to NRC (2001) equations to meet or exceed the nutritional requirements of a cow weighing 660 kg, producing 42 kg of milk with 3.5% fat and 3.0% true protein.

In the DGC (dry ground corn) treatment, corn kernels were ground using the on-farm hammer mill equipped with a 3-mm screen, operating at 975 g. The steam-flaking process involved steaming whole corn kernels for approximately 60 minutes in a vertical steam chamber to achieve a moisture content of 18 to 20%. The steamed corn was then passed through rollers at a temperature of 105°C, producing flakes with an approximate bulk density of 400 g/L.

RESULTS AND DISCUSSION:

In this study, on average, dry matter intake (DMI) decreased from 14 kg to 9 kg from one week before calving to the day of calving. Regardless of corn grain processing method, cows fed with the SLW (slow rate of concentrate feeding) strategy had higher forage intake, which was accompanied by lower concentrate intake compared to the FAS (fast rate) group. Total DMI was greater in cows fed with the FAS strategy compared to those on the SLW diet. The main difference in nutrient composition among the diets was in the starch, NDF (neutral detergent fiber), and CP (crude protein) contents. Therefore, the difference in feed intake was primarily due to variations in the carbohydrate fraction, which may be attributed to differences in dietary NDF content and NDF intake. Additionally, cows under the SLW strategy consumed less dietary protein during the first 16 days of lactation (approximately 0.5 kg/day) compared to those in the FAS group. This difference may have affected feed intake, as it has been reported that DMI increases with increased dietary protein content in lactating cows.

Although cows fed with the SLW (slow-loading) strategy produced 0.8 kg/day less milk compared to those fed with the FAS (fast-loading) strategy, the change in concentrate feeding rate strategy had no significant effect on daily milk yield (P = 0.11). Considering the significant impact of feeding strategy on DMI, the average milk yield during the first 64 days of lactation was numerically greater in cows fed with the FAS strategy compared to the SLW group.

Previous studies have reported that milk fat concentration improved in weeks 4 and 5 with a gradual increase in concentrate feeding. Specifically, milk fat concentration in the treatment group receiving 0.5 kg/day of concentrate was 0.36 to 0.47 percentage units lower than the group receiving 0.3 kg/day. These results can be attributed to the higher forage proportion in the diet when less concentrate was fed. A similar reduction in milk protein concentration (by 0.1 g/kg) due to high-fiber diets has also been observed in forage silage-based rations. The slightly lower milk protein concentration observed in the SLW group at 16 and 32 days in milk is likely due to lower DMI and reduced microbial protein synthesis. 
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An interaction effect of feeding strategy × day was detected for milk lactose production, such that cows fed with the FAS strategy tended to have increased milk lactose compared to those fed with the SLW strategy. It has been reported that milk lactose production in cows fed higher amounts of concentrate was greater than in cows fed lower amounts of concentrate during weeks 2 to 15 postpartum, due to higher blood glucose concentration. Total DMI was increased throughout the entire period when cows were fed SFC compared to DGC (21.6 vs. 23.8 kg/day). The authors of this study predicted that the higher DMI in SFC could be related to the greater digestibility of starch in the rumen. Correspondingly, cows fed the SFC-based diet had higher milk production (P = 0.05); however, the indices of ECM and 3.5% FCM showed no difference between the two treatments, SFC and DGC. It was previously reported that there was no difference in milk production in cows producing less than 30 kg/day when fed steam-flaked corn and dry-rolled corn. Considering the milk production over 30 liters in this study, the difference in the effect of steam-flaking processing can be attributed to the higher starch digestibility throughout the digestive tract, leading to greater energy availability from the grain.

In this study, milk protein tended to increase during SFC feeding compared to DGC (P = 0.07). Previous studies have attributed the increase in milk protein during SFC feeding to higher amounts of rumen-fermentable carbohydrates and non-structural carbohydrate (NSC) content in the diet. In our study, the increased milk protein production in cows fed SFC diets was likely due to a greater supply of gluconeogenic precursors and increased microbial protein synthesis resulting from enhanced starch digestibility. Additionally, cows fed SFC diets had higher milk lactose concentration and production compared to DGC. This is attributed to increased production of volatile fatty acids (VFAs), especially propionic acid, and greater nutrient absorption in the mammary gland.

Milk fatty acids (FA) are produced through the diet, mammary glands (de novo synthesis), rumen (biohydrogenation, bacterial digestion, and synthesis), and body fat mobilization. When cows are in negative energy balance, the contribution of FA from body reserves can reach up to 20% of milk FA. The greatest changes in milk FA profile occur during negative energy balance from week 1 to 6 after calving, while the FA composition of milk remains relatively stable between weeks 12 and 21 post-calving. De novo synthesis of fatty acids accounts for approximately 40% of milk fat throughout the lactation period, but preformed FA make up a larger portion of total milk FA in early lactation. In this study, cows fed with the SLW strategy had higher concentrations of preformed FA in their milk up to 32 days in milk (DIM). In our study, the increase in preformed FA in milk fat can be attributed to increased fat tissue mobilization in cows fed SLW compared to those fed FAS.

The total concentration of trans-18:1 and trans-11 18:1 fatty acids in milk was higher in the FAS feeding strategy. It has been previously reported that the duodenal flow of total trans-18:1 FA in cows fed a diet containing 75% concentrate led to a twofold increase in the concentration of total trans-18:1 FA in milk fat. Meanwhile, the concentration of de novo and mixed FA (P < 0.01) as well as preformed FA (P = 0.08) increased in the SLW strategy. The NDF and starch contents of the diet play important roles in ruminal biohydrogenation by altering the ruminal pH pattern. Food-origin triglycerides undergo ruminal lipolysis, and the FA are extensively biohydrogenated in the rumen, resulting in the synthesis of a wide range of biohydrogenation intermediates, which can exit the rumen and be absorbed in the small intestine. Among many factors influencing the extent of ruminal FA biohydrogenation, the concentrate ratio seems to have a greater effect, leading to increased synthesis of trans-FA intermediates (e.g., trans-10 18:2, trans-9 cis-11 18:2, and trans-10 cis-12 18:2). Similarly, diets with higher concentrate levels have been observed to increase trans-10 18:1 relative to trans-11 18:1 in rumen fluid; therefore, the shift in biohydrogenation from trans-11 to trans-10 has been associated with reduced milk fat.

Heat processing of grains increases the surface area of the grains and causes starch gelatinization due to denaturation of the protein matrix, which improves starch fermentation in the rumen. Greater starch fermentability in the rumen can alter fatty acid biohydrogenation pathways and increase the synthesis of specific isomers of trans-18:1. In the present study, the ratio of trans-18:1 FA did not change with feeding SFC or DGC diets. Starch degradability in the rumen increases with SFC feeding compared to the DGC-based diet (the starch digestibility of SFC under laboratory conditions is 12.4% higher than DGC). However, in this study, no changes in the rumen environment were observed when feeding SFC compared to DGC.

The average body weight (BW) and body condition score (BCS) of the cows at calving were 665 kg and 3.8, respectively. In all experimental groups, the BCS decreased by an average of 1.0 unit during the first 64 days of lactation, with a more pronounced weight loss in the SLW treatment (34.9 kg and 35.2 kg for FAS and SLW, respectively). The greater weight loss in the SLW group, especially during the first weeks after calving, was likely due to lower dry matter intake (DMI) and consequently lower energy intake. This finding highlights the importance of DMI in maximizing energy intake during the early postpartum period. Furthermore, the increased BW loss in the SLW strategy was probably due to greater physical fill of the digestive tract along with greater mobilization of body reserves, leading to reduced energy requirements for maintenance compared to the FAS strategy. This effect was more evident on day 16 of lactation and was attributed to the higher forage-to-concentrate ratio in the diet, which resulted in lower energy intake. Overall, the FAS strategy improved energy balance compared to SLW. Regarding grain processing, previous reports indicated that feeding at least 21% cracked or steam-flaked corn in early lactation did not affect BW or BCS. Considering that 56% of the concentrate in this experiment consisted of grains, no changes in BW or BCS were observed.

An interaction effect between the concentrate feeding rate and the corn grain processing method was observed on plasma glucose concentration. Feeding steam-flaked corn (SFC) increased plasma glucose concentration compared to dry ground corn (DGC), especially when used in the FAS (fast additive supplementation) feeding strategy. Postpartum FAS concentrate, compared to SLW (slow additive supplementation) concentrate, may increase volatile fatty acid (VFA) concentrations in the rumen, particularly propionate, which supports gluconeogenesis and positively improves blood glucose concentration. Plasma concentrations of beta-hydroxybutyrate (BHB) and non-esterified fatty acids (NEFA) increased with the SLW treatment throughout the experiment. This suggests that the SLW treatment was associated with a more negative energy balance.

CONCLUSIONS:

Cows fed simultaneously with the FAS (fast additive supplementation) strategy and steam-flaked corn (SFC) had higher blood glucose levels. Implementing a rapid increase in concentrate feeding rate after calving improved dry matter intake (DMI), milk production, and milk lactose yield, but was accompanied by reductions in body condition score (BCS) and body weight (BW) during the first 64 days of lactation. Additionally, FAS increased the total concentration of trans-11 18:1 and 18:1 fatty acids in milk fat compared to the SLW (slow additive supplementation) strategy, while the proportions of de novo, mixed, and preformed fatty acids were higher in SLW. Dry matter intake and milk production were influenced by the corn processing method as lactation progressed, resulting in a tendency for increased protein and lactose concentrations in milk throughout the entire period. These results suggest that when cows are fed with the SLW increasing rate, corn processing may not be an effective tool to improve production responses during the first 64 days in milk (DIM).

Doi: https://doi.org/۱۰.۳۱۶۸/jds.۲۰۲۰-۱۹۰۱۵

Razzaghi, A., J. Drackley, and M. Malekkhahi, Concentrate allowance and corn grain processing influence milk production, body reserves, milk fatty acid profile, and blood metabolites of dairy cows in the early postpartum period. Journal of Dairy Science, ۲۰۲۱. ۱۰۴(۵): p. ۵۴۷۹-۵۴۹۲.