Effect of dietary crude protein degradability and corn processing on lactation performance and milk protein composition and stability

Abstract

The present study aimed to evaluate the effect of crude protein degradability and corn processing on lactation performance, milk protein composition, milk ethanol stability (MES), heat coagulation time (HCT) at 140°C, and the efficiency of N utilization for dairy cows. Twenty Holstein cows with an average of 162 ± 70 d in milk, 666 ± 7 kg of body weight, and 36 ± 7.8 kg/d of milk yield (MY) were distributed in a Latin square design with 5 contemporaneous balanced squares, 4 periods of 21 d, and 4 treatments (factorial arrangement 2 × 2). Treatment factor 1 was corn processing [ground (GC) or steam-flaked corn (SFC)] and factor 2 was crude protein (CP) degradability (high = 10.7% rumen-degradable protein and 5.1% rumenundegradable protein; low = 9.5% rumen-degradable protein and 6.3% rumen-undegradable protein; dry matter basis). A significant interaction was observed between CP degradability and corn processing on dry matter intake (DMI). When cows were fed GC with low CP degradability, DMI increased by 1.24 kg/d compared with cows fed GC with high CP degradability; however, CP degradability did not change DMI when cows were fed SFC. Similar interactions were observed for MY, HCT, and lactose content. When cows were fed GC diets, high CP degradability reduced MY by 2.3 kg/d, as well as HCT and lactose content, compared with low CP degradability. However, no effect of CP degradability was observed on those variables when cows were fed SFC diets. The SFC diets increased dry matter and starch total-tract digestibility and reduced β-casein (CN) content (% total milk protein) compared with GC diets. Cows fed low-CP degradability diets had higher glycosylated κ-CN content (% total κ-CN) and MES, as well as milk protein content, 3.5% fatcorrected milk, and efficiency of N for milk production, than cows fed high-CP degradability diets. Therefore, GC and high-CP degradability diets reduced milk production and protein stability. Overall, low CP degradability increased the efficiency of dietary N utilization and MES, probably due to changes in casein micelle composition, as CP degradability or corn processing did not change the milk concentration of ionic calcium. The GC diets increased β-CN content, which could contribute to reducing HTC when cows were fed GC and high-CP degradability diets.

Synchronization of rumen degradable protein with non-fiber carbohydrate on microbial protein synthesis and dairy ration digestibility

“…Information concerning the RDPR and NFC in dairy feedstuffs has mainly been investigated in developed countries, which use different feedstuffs than the tropical dairy ration [19][20][21]. Moreover, synchronization index assessments conducted in a temperate region may not be suitable for application to tropical conditions.…”

The effect of diet restriction on raw milk stability: a meta-analytical approach

“…The reduction of the acidity as a function of the magnitude of the feed restriction may be related to the reduction of the protein concentration, which together with minerals such as phosphates and dissolved gasses contributes to the natural acidity of milk (Schmidt et al, 1996). In the case of unbalanced diets with excess protein in relation to energy, the low stability observed (Marques et al, 2010b;Schmidt, 2015) might be related to an excess of rumen degradable protein, which, in turn, is related to the lower glycosylation of κ-casein, reducing milk stability, as verified by Martins et al (2019).…”

“…In the case of unbalanced diets with excess protein in relation to energy, the low stability observed (Marques et al ., 2010b; Schmidt, 2015) might be related to an excess of rumen degradable protein, which, in turn, is related to the lower glycosylation of κ-casein, reducing milk stability, as verified by Martins et al . (2019).…”

“…Milk ethanol stability (MES) is influenced by several factors related to farm, environment, animals, feeding practices (Marques et al ., 2010b; Martins et al ., 2019) and animal health (Marques et al ., 2011). It is already known that the raw milk stability decreases with reducing availability of pasture plus supplement (Fruscalso et al ., 2013) or with TMR (Zanela et al ., 2006; Gabbi et al ., 2015) Decreased MES is also linked to a lower supply of nutrients (Stumpf et al ., 2013) or an imbalance between nutrients such as energy and protein (Marques et al ., 2010b; Gabbi et al ., 2015; Schmidt, 2015), as well as with an increase in the fiber content of forages provided (Barchiesi et al ., 2007).…”

Effect of Dietary Rumen-Degradable Starch to Rumen-Degradable Protein Ratio on In Vitro Rumen Fermentation Characteristics and Microbial Protein Synthesis

“…Therefore, more attention should be paid to the characteristics of energy and N sources used in diet [ 9 ]. Recent studies have demonstrated that rumen-degradable starch (RDS) and RDP could affect rumen fermentation, microbial community compositions, and MCPS [ 10 , 11 , 12 , 13 ]. Since MCPS was recognized as the important criterion for determining the degree of dietary synchronization [ 14 , 15 , 16 ], it is reasonable to infer that the RDS and RDP may be more effective indicators for evaluating the synchrony of energy and N supply.…”