Heat stress-associated changes in the intestinal barrier, inflammatory signals, and microbiome communities in dairy calves.

Recent studies indicate that heat stress pathophysiology is associated with intestinal barrier dysfunction, local and systemic inflammation, and gut dysbiosis. However, inconclusive results and a poor description of tissue-specific changes must be addressed to identify potential intervention targets against heat stress illness in growing calves. Therefore, the objective of this study was to evaluate components of the intestinal barrier, pro- and anti-inflammatory signals, and microbiota community composition in Holstein bull calves exposed to heat stress. Animals (mean age = 12 wk old; mean body weight = 122 kg) penned individually in temperature-controlled rooms were assigned to (1) thermoneutral conditions (constant room temperature at 19.5°C) and restricted offer of feed (TNR, n = 8), or (2) heat stress conditions (cycles of room temperatures ranging from 20 to 37.8°C) along with ad libitum offer of feed (HS, n = 8) for 7 d. Upon treatment completion, sections of the jejunum, ileum, and colon were collected and snap-frozen immediately to evaluate gene and protein expression, cytokine concentrations, and myeloperoxidase activity. Digesta aliquots of the ileum, colon, and rectum were collected to assess bacterial communities. Plasma was harvested on d 2, 5, and 7 to determine cytokine concentrations. Overall, results showed a section-specific effect of HS on intestinal integrity. Jejunal mRNA expression of TJP1 was decreased by 70.9% in HS relative to TNR calves. In agreement, jejunal expression of heat shock transcription factor-1 protein, a known tight junction protein expression regulator, decreased by 48% in HS calves. Jejunal analyses showed that HS decreased concentrations of IL-1α by 36.6% and tended to decrease the concentration of IL-17A. Conversely, HS elicited a 3.5-fold increase in jejunal concentration of anti-inflammatory IL-36 receptor antagonist. Plasma analysis of pro-inflammatory cytokines showed that IL-6 decreased by 51% in HS relative to TNR calves. Heat stress alteration of the large intestine bacterial communities was characterized by increased genus Butyrivibrio_3, a known butyrate-producing organism, and changes in bacteria metabolism of energy and AA. A strong positive correlation between the rectal temperature and pro-inflammatory Eggerthii spp. was detected in HS calves. In conclusion, this work indicates that HS impairs the intestinal barrier function of jejunum. The pro- and anti-inflammatory signal changes may be part of a broader response to restore intestinal homeostasis in jejunum. The changes in large intestine bacterial communities favoring butyrate-producing organisms (e.g., Butyrivibrio spp.) may be part of a successful response to maintain the integrity of the colonic mucosa of HS calves. The alteration of intestinal homeostasis should be the target for heat stress therapies to restore biological functions, and, thus highlights the relevance of this work.

Bacterial community structure in the rumen and hindgut is associated with nitrogen efficiency in Holstein cows.

Nitrogen efficiency (Neff; milk N/N intake) in dairy cows is limited and most of the consumed N is excreted in manure. Despite the crucial role of the gastrointestinal microbiome on N metabolism, associations between bacterial communities at different sections and Neff are not fully elucidated. Enhanced understanding of host-microbiome interactions can provide insights to improve Neff in dairy cows. Twenty-three Holstein cows were selected, and their Neff were determined using a N balance approach. From the cohort of cows, six cows were classified as low Neff and five cows as high Neff and their rumen and fecal bacterial communities were profiled using amplicon sequence variants (ASV) based on 16S rRNA gene sequencing. Then, relationships between differentially abundant bacterial features and Neff were evaluated. Neff in low and high cows averaged 22.8 and 30.3%, respectively. With similar N intake, high Neff cows wasted less N in manure compared to low Neff cows (P < 0.01, 11.0 ± 0.59 vs 14.3 ± 0.54 g of N/kg of milk). Rumen fermentation and plasma profiles were similar between Neff groups, but for plasma Gln which was greater (P = 0.02) in high compared to low Neff cows. In both rumen and feces, the phylogenetic composition of the bacterial communities was similar (P ≥ 0.65) between Neff groups, but differences were observed at the species -level (amplicon sequence variants). In the rumen, differentially abundant species from the genus Prevotella showed strong positive correlations with Neff, whereas in feces, differentially abundant species from the class Clostridia showed strong negative correlations with Neff. Our results revealed that Holstein cows with divergent Neff display distinctive bacterial community structure at the species-level in both the rumen and feces. Strong correlations between differentially abundant species and Neff in both sample sites, support the importance of the rumen bacterial composition on productive responses and suggest a more relevant role of the hindgut microbiome. Targeting both pre- and post-gastric bacterial communities may provide novel opportunities to enhance Neff in dairy cows.

Lactation responses and amino acid utilization of dairy cows fed low-fat distillers dried grains with solubles with or without rumen-protected lysine supplementation.

The objective of this study was to evaluate the effects of feeding different amounts of low-fat distillers dried grains with solubles (DDGS) in diets with or without supplementation of rumen-protected Lys (RPL) on lactation responses and AA utilization. Eight multiparous Holstein cows averaging 188 ± 13 DIM were assigned to a replicated 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments. Dietary treatments were as follows: (1) 15% low-fat DDGS, (2) 15% low-fat DDGS plus RPL, (3) 30% low-fat DDGS, and (4) 30% low-fat DDGS plus RPL. Periods lasted 21 d, with the last 3 d for data collection. Basal diets (without RPL) were formulated using the Cornell-Penn-Miner Dairy model [Cornell University (Ithaca, NY), University of Pennsylvania (Philadelphia), and the W. H. Miner Agricultural Research Institute (Chazy, NY)] to be isonitrogenous (16.9% crude protein) and isocaloric (2.63 Mcal/kg) and inclusion of low-fat DDGS increased at the expense of corn and soybean meal. Inclusion rate of low-fat DDGS and RPL supplementation had no effect on dry matter intake and milk yield, averaging 25.3 ± 0.97 kg/d and 26.9 ± 1.94 kg/d, respectively (means ± standard error of the means). Milk fat and lactose concentrations were unaffected by treatments but milk protein concentration decreased in cows fed treatments with 30% low-fat DDGS compared with those fed treatments with 15% low-fat DDGS (3.49 vs. 3.40 ± 0.12%). Updated predictions from the Cornell-Penn-Miner Dairy model showed a decrease of 25 g of metabolizable protein Lys in cows fed treatments with 30% low-fat DDGS. Compared with cows fed treatments with 15% low-fat DDGS, cows fed treatments with 30% low-fat DDGS had a marked increase in extraction efficiency (49.4 vs. 61.4 ± 2.51%) and a tendency to increase milk protein concentration (3.41 vs. 3.48 ± 0.12%) with RPL supplementation, which supported that Lys supply was inadequate. Despite differences observed in milk protein concentration, milk protein yield was similar across treatments and averaged 0.92 ± 0.06 kg/d. Lack of response on arterial Lys concentration with RPL supplementation leads us to suspect that the RPL product delivered a lower amount of metabolizable Lys than expected. Based on extraction efficiencies, Lys, Arg, and Phe were the first 3 limiting AA across treatments. Supplementation of rumen-protected AA has the potential to be an effective nutritional strategy to supply limiting AA; however, accurate information on the bioavailability of the AA is needed.

Ruminal degradation and intestinal digestibility of protein and amino acids in high-protein feedstuffs commonly used in dairy diets.

A study was conducted to determine the rumen degradation and intestinal digestibility of crude protein (CP) and AA, and AA composition of the rumen-undegradable protein (RUP) from 3 sources of blood meal (BM1, BM2, and BM3), canola meal (CM), low-fat distillers dried grains with solubles (LFDG), soybean meal (SBM), and expeller soybean meal (ESBM). Two Holstein cows fitted with ruminal and proximal duodenal cannulas were used for in situ incubation of 16h and for the mobile bag technique. To correct for bacterial contamination of the RUP, 2 methods were used: purines and DNA as bacterial markers. Ruminal degradations of CP were 85.3, 29.8, 40.7, 75.7, 76.9, 68.8, and 37.0 ± 3.93% for BM1, BM2, BM3, CM, LFDG, SBM, and ESBM, respectively. Ruminal degradation of both total essential AA and nonessential AA followed a similar pattern to that of CP across feedstuffs. Based on the ratio of AA concentration in the RUP to AA concentration in the original feedstuff, ruminal incubation decreased (ratio <1) the concentrations of His, Lys, and Trp, and increased (ratio >1) the concentrations of Ile and Met across feedstuffs. Compared with purines, the use of DNA as bacterial marker resulted in a higher estimate of bacterial CP contamination for CM and lower estimates for LFDG and ESBM. Intestinal digestibility of RUP could not be estimated for BM1, BM3, and SBM due to insufficient recovery of residue. For the remaining feedstuffs, intestinal digestibility of RUP was highest for ESBM, followed by BM2 and LFDG, and lowest for CM: 98.8, 87.9, 89.7, and 72.4 ± 1.40%, respectively. Intestinal absorbable dietary protein was higher for BM2 compared with CM and LFDG, at 61.7, 17.9, and 20.7 ± 2.73% CP, respectively. As prices fluctuate, intestinal absorbable protein or AA may be used as a tool to aid in the selection among feedstuffs with different protein quality.

Performance of dairy cows fed silage and grain produced from second-generation insect-protected (Bacillus thuringiensis) corn (MON 89034), compared with parental line corn or reference corn.

Corn grain and corn silage are major feed components in lactating dairy cow rations. Bacillus thuringiensis (B.t.) is a naturally occurring soil bacterium that produces a protein that is toxic to lepidopteran insects that may damage plant tissues and reduce corn quality and yields. During each of the four 28-d periods, cows were offered 1 of 4 rations in which the corn grain and silage originated from different corn hybrids: a nontransgenic corn control (from hybrid DKC63-78; Monsanto Co., St. Louis, MO), a B.t. test substance corn (MON 89034 in hybrid DKC63-78; Monsanto Co.), and 2 commercial nontransgenic reference (Ref) hybrids: DKC61-42 (Ref 1) and DKC62-30 (Ref 2; Monsanto Co.). Sixteen multiparous Holstein cows averaging 110 ± 21 d in milk and weighing 684 ± 62.3 kg were blocked by days in milk and milk yield and randomly assigned to one of four 4 × 4 Latin squares. Diets were formulated to contain 36.4% corn silage and 16.3% corn grain. Dry matter intake was greater for cows consuming B.t. corn (26.6 ± 0.59 kg/d) compared with the control, Ref 1, and Ref 2 corn diets (25.4, 25.0, and 25.6 ± 0.59 kg/d, respectively). Milk yield, fat yield, and percentage of fat (36.8 ± 0.98 kg/d, 1.22 ± 0.05 kg/d, and 3.3 ± 0.10%), milk protein yield and percentage of protein (1.11 ± 0.03 kg/d and 3.01 ± 0.05%), milk urea nitrogen concentration (14.01 ± 0.49 mg/dL), and 3.5% fat-corrected milk yield (35.7 ± 1.07 kg/d) were not different across treatments. The results from this study show that lactating dairy cows that consume B.t. corn (MON 89034) do not differ from lactating dairy cows that consume nontransgenic corn in milk yield, 3.5% fat-corrected milk per unit of dry matter intake, or milk components.

Evaluation of rumen-protected lysine supplementation to lactating dairy cows consuming increasing amounts of distillers dried grains with solubles.

Twenty multiparous Holstein cows were used in four 5 × 5 Latin squares to determine the effects of feeding increasing amounts of distillers dried grains with solubles (DDGS) in diets with or without the supplementation (60 g/d) of a rumen-protected Lys (RPL) product (AminoShure-L, 38% l-Lys; Balchem Encapsulates, New Hampton, NY) on milk yield and composition and plasma concentration of AA. Dietary treatments were (1) control (CON; no DDGS), (2) 10% DDGS (10DG), (3) 20% DDGS (20DG), (4) 10% DDGS plus RPL (10DGRPL), and (5) 20% DDGS plus RPL (20DGRPL). Diets were formulated using the Cornell-Penn-Miner Dairy model (CPM v3.0; http://cahpwww.vet.upenn.edu/node/77) to provide a predicted decreasing supply of Lys (117, 99, and 91% of requirements) for the CON, 10DG, and 20DG diets, respectively. Addition of RPL to the 10DG and 20DG diets (unsupplemented diets) resulted in 2 additional treatments, 10DGRPL and 20DGRPL diets, respectively. The 10DGRPL and 20DGRPL diets met 110 and 100% of the Lys requirements, respectively. Periods lasted 21d, with the last 3d for data collection. Compared with cows fed the CON diet, cows fed diets with DDGS had a similar dry matter intake (DMI; 25.4 ± 0.88 kg/d), milk yield (30.7 ± 1.67 kg/d), and composition, except for protein percentage, which was higher (3.15 vs. 3.21 ± 0.05%) and resulted in higher (0.94 vs. 1.00 ± 0.05 kg/d) protein yield by cows fed diets containing 20% DDGS. Unexpectedly, despite diets being formulated based on predicted DMI of 23.3 kg/d and milk yield of 38.5 kg/d, cows had a greater DMI and lower milk yield across all treatments, which resulted in diets that were predicted by CPM Dairy to supply sufficient amounts of Lys (140, 118, and 104% of requirement for the CON, 10 DG, and 20 DG diet, respectively) and consequently, supplementation with RPL did not have an effect on milk production or composition. Plasma concentration of Lys decreased (11.8%) as DDGS inclusion increased. For other essential AA, plasma concentrations of cows fed diets with DDGS were lower for Arg, His, and Val and greater for Leu and Met compared with cows fed the CON diet. Supplementation with RPL failed to decrease the plasma concentration of other essential AA, which provides support that Lys was not limiting.