This study was conducted to investigate the nutrient digestibility and lactation performance when alfalfa was replaced with rice straw or corn stover in the diet of lactating cows. Forty-five multiparous Holstein dairy cows were blocked based on days in milk (164 ± 24.8 d; mean ± standard deviation) and milk yield (29.7 ± 4.7 kg; mean ± standard deviation) and were randomly assigned to 1 of 3 treatments. Diets were isonitrogenous, with a forage-to-concentrate ratio of 45:55 [dry matter (DM) basis] and contained identical concentrate mixtures and 15% corn silage, with different forage sources (on a DM basis): 23% alfalfa hay and 7% Chinese wild rye hay (AH), 30% corn stover (CS), and 30% rice straw (RS). The experiment was conducted over a 14-wk period, with the first 2 wk for adaptation. The DM intake of the cows was not affected by forage source. Yield of milk, milk fat, protein, lactose, and total solids was higher in cows fed diets of AH than diets of RS or CS, with no difference between RS and CS. Contents of milk protein and total solids were higher in AH than in RS, with no difference between CS and AH or RS. Feed efficiency (milk yield/DM intake) was highest for cows fed AH, followed by RS and CS. Cows fed AH excreted more urinary purine derivatives, indicating that the microbial crude protein yield may be higher for the AH diet than for RS and CS, which may be attributed to the higher content of fermentable carbohydrates in AH than in RS and CS. Total-tract apparent digestibilities of all the nutrients were higher in cows fed the AH diet than those fed CS and RS. The concentration of rumen volatile fatty acids was higher in the AH diet than in CS or RS diets, with no difference between CS and RS diets. When the cereal straw was used to replace alfalfa as a main forage source for lactating cows, the shortage of fermented energy may have reduced the rumen microbial protein synthesis, resulting in lower milk protein yield, and lower nutrient digestibility may have restricted milk production.

Heat stress affects feed intake, milk production, and endocrine status in dairy cows. The temperature-humidity index (THI) is employed as an index to evalu

Ferulic acid (FA) is one of the most abundant hydroxycinnamic acids in the plant world, especially in the cell wall of grain bran, in comparison with forage and crop residues. Previous studies noted that FA was mainly linked with arabinoxylans and lignin in plant cell walls in ester and ether covalent forms. After forages were ingested by ruminant animals or encountered rumen microbial fermentation in vitro, these cross-linkages form physical and chemical barriers to protect cell-wall carbohydrates from microbial attack and enzymatic hydrolysis. Additionally, increasing studies noted that FA presented some toxic effect on microbial growth in the rumen. In recent decades, many studies have addressed the relationships of ester and/or ether-linked FA with rumen nutrient digestibility, and there is still some controversy whether these linkages could be used as a predicator of forage digestibility in ruminants. The authors in this review summarized the possible relationships between ester and/or ether-linked FA and fiber digestion in ruminants. Rumen microbes, especially bacteria and fungi, were found capable of breaking down the ester linkages within plant cell walls by secreting feruloyl and p-coumaroyl esterase, resulting in the release of free FA and improvement of cell wall digestibility. The increasing evidence noted that these esterases secreted by rumen microbes presented synergistic effects with xylanase and cellulase to effectively hydrolyze forage cell walls. Some released FA were absorbed through the rumen wall directly and entered into blood circulation and presented antioxidant effects on host animals. The others were partially catabolized into volatile fatty acids by rumen microbes, and the possible catabolic pathways discussed. To better understand plant cell wall degradation in the rumen, the metabolic fate of FA along with lignin decomposition mechanisms are needed to be explored via future microbial isolation and incubation studies with aims to maximize dietary fiber intake and enhance fiber digestion in ruminant animals.

Heat stress (HS) negatively affects various industries that rely on animal husbandry, particularly the dairy industry. A better understanding of metabolic responses in HS dairy cows is necessary to elucidate the physiological mechanisms of HS and offer a new perspective for future research. In this paper, we review the current knowledge of responses of body metabolism (lipid, carbohydrate, and protein), endocrine profiles, and bovine mammary epithelial cells during HS. Furthermore, we summarize the metabolomics and proteomics data that have revealed the metabolite profiles and differentially expressed proteins that are a feature of HS in dairy cows. Analysis of metabolic changes and “omics” data demonstrated that HS is characterized by reduced lipolysis, increased glycolysis, and catabolism of amino acids in dairy cows. Here, analysis of the impairment of immune function during HS and of the inflammation that arises after long-term HS might suggest new strategies to ameliorate the effects of HS in dairy production.