Recovery of absorptive function of the reticulo-rumen and total tract barrier function in beef cattle after short-term feed restriction

Development of an experimental model for liver abscess induction in Holstein steers using an acidotic diet challenge and bacterial inoculation

Holstein steers (n = 40; initial BW = 84.9 ± 7.1 kg) were used to study the genesis of liver abscesses (LA) using an acidotic diet challenge with or without intraruminal bacterial inoculation. Steers were housed in individual pens inside a barn and randomly assigned to one of three treatments: (1) low-starch control diet comprised primarily of dry-rolled corn and wet corn gluten feed (CON); (2) high-starch acidotic diet with steam-flaked corn (AD); or (3) acidotic diet plus intraruminal inoculation with Fusobacterium necrophorum subsp. necrophorum (9.8 × 108 colony forming units [CFU]/mL), Trueperella pyogenes (3.91 × 109 CFU/mL), and Salmonella enterica serovar Lubbock (3.07 × 108 CFU/mL), previously isolated from LA (ADB). Steers in AD and ADB were fed the acidotic diet for 3 d followed by 2 d of the CON diet, and this cycle was repeated four times. On day 23, ADB steers were intraruminally inoculated with the bacteria. At necropsy, gross pathology of livers, lungs, rumens, and colons was noted. Continuous data were analyzed via mixed models as repeated measures over time with individual steer as the experimental unit. Mixed models were also used to determine the difference in prevalence of necropsy scores among treatments. Ruminal pH decreased in AD and ADB steers during each acidotic diet cycle (P ≤ 0.05). LA prevalence was 42.9% (6 of 14) in ADB vs. 0% in AD or CON treatments (P < 0.01). Ruminal damage was 51.1% greater in ADB than in AD (P ≤ 0.04). Culture of LA determined that 100% of the abscesses contained F. necrophorum subsp. necrophorum, 0% contained T. pyogenes, 50% contained Salmonella, and 50% contained a combination of F. necrophorum subsp. necrophorum and Salmonella. The F. necrophorum subsp. necrophorum was clonally identical to the strain used for the bacterial inoculation based on phylogenetic analysis of the whole genome. This experimental model successfully induced rumenitis and LA in Holstein steers and confirms the central dogma of LA pathogenesis that acidosis and rumenitis lead to the entry of F. necrophorum into the liver to cause abscesses. Our findings suggest that an acidotic diet, in conjunction with intraruminal bacterial inoculation, is a viable model to induce LA. Further research is needed to determine the repeatability of this model, and a major application of the model will be in evaluations of novel interventions to prevent LA.

Effects of flavoring additives on feed intake, growth performance, temperament, and markers of immune function for newly received feedlot cattle

Ninety Angus × Hereford steers (259.9 ± 36.18 kg body weight [BW]) were used in a 56-d experiment to assess the effects of flavoring additives on feed intake, and stress and immune response of newly received feedlot cattle. Steers were homogenously distributed by BW into six pens equipped with an individual feed intake monitoring system, and pen was randomly assigned to one of three treatments (15 heads per pen; 30 heads per treatment): a standard feedlot receiving diet (CT), or the same diet with a flavoring additive comprised of either sweeteners (Luctarom Feedlot, SW) or a mix of basic tastes (Luctarom Feedlot Mix, MX) at 1 kg/mT. Pens were equipped with a feed intake monitoring system, while BW, chute behavior, flight speed, blood and saliva samples were collected bi-weekly, and hair samples were collected at 4-wk intervals during the study. Data were analyzed using a mixed-effects model for a pen study using individual animal records with repeated measures. There was a treatment × week interaction (P < 0.01) where meal duration was greater in SW steers than MX and CT on week 3, and then CT on weeks 7 and 8. A trend for treatment × week interaction (P = 0.06) showed that the number of visits per day tended to be greater in SW than MX steers on weeks 4 and 5, and it tended to be greater in SW than MX and CT on week 5. The concentration of IL-6 was greater (P < 0.01) on days 1 and 28 than on day 14. The IgM concentration was greater (P < 0.01) on day 1 compared to days 14, 28, and 56. The concentration of haptoglobin was greater (P < 0.01) on 14 than days 28, 42, and 56, and it was greater (P < 0.01) on day 1 than days 42 and 56. The concentration of serum amyloid A was greater (P < 0.01) on day 1 compared to the rest of sampling days. Fibrinogen concentration was greater (P < 0.01) on day 1 compared to days 14 and 42. The neutrophil-to-lymphocyte ratio was greater (P < 0.01) on days 42 and 56 compared to days 1 and 28, and greater (P < 0.01) on day 14 compared to day 28. Hair and saliva cortisol concentrations were lower (P < 0.01) on day 56 compared to days 1 and 28, respectively. The use of flavoring additives, particularly when based on sweeteners (SW), caused some changes in the feeding pattern of newly received steers. These changes, however, were not consistent over the 56-d feeding period and were not accompanied by a change in growth performance, temperament, biomarkers of stress, inflammation, or immune function.

Feeding colostrum and transition milk facilitates digestive tract functionality recovery from feed restriction and fasting of dairy calves

The objective of this study was to evaluate the digestive tract recovery and metabolism of feeding either bovine colostrum (BC), transition milk (TM), or milk replacer (MR) after an episode of feed restriction and fasting (FRF) in dairy calves. Thirty-five Holstein male calves (22 ± 4.8 d old) were involved in a 50-d study. After 3 d of feeding 2 L of rehydration solution twice daily and 19 h of fasting (d 1 of study), calves were randomly assigned to one of the 5 feeding treatments (n = 7): calves were offered either pooled BC during 4 (C4) or 10 (C10) days, pooled TM during 4 (TM4) or 10 (TM10) days, or MR for 10 d (CTRL) at the rate of 720 g/d DM content. Then, all calves were fed the same feeding program, gradually decreasing MR from 3 L twice daily to 2 L once daily at 12.5% DM until weaning (d 42), and concentrate feed, water, and straw were offered ad libitum until d 50. Citrulline, Cr-EDTA, β-hydroxybutyrate (BHB), and nonesterified fatty acids (NEFA) in serum and complete blood count (CBC) were determined on d -3, 1, 2, 5, and 11 relative to FRF, except BHB and NEFA at d -3. Volatile fatty acids (VFA), lactoferrin (LTF), IgA, and microbiota (Firmicutes to Bacteroidetes ratio and Fecalis prausnitzii) were analyzed in feces on d 5 and 11 before the morning feeding. Health scores were recorded daily from d -3 to d 14 as well as d 23 and 30. Feed concentrate, MR, and straw intake were recorded daily, and body weight on d -3, 1, 2, 5, and 11 and weekly afterward. Calf performance, intake, serum Cr-EDTA, CBC, fecal LTF concentrations and microbiota parameters were similar among treatments throughout the study. Serum NEFA concentrations were greater in TM4, TM10 and C10 calves compared with the CTRL ones from d 2 to 11, and after the FRF, serum concentrations of BHB were lower in CTRL calves than in the other treatments, and on d 11, serum BHB concentrations in the long treatments (C10 and TM10) remained greater than those in the shorter ones (C4 and TM4) and CTRL. Serum citrulline concentrations were similar on d -3 and 1 in all treatments, but they were greater in C4, C10, TM4, and TM10 on d 2 and 5, and on d 11 they were only greater in C10 and TM10 than in CTRL calves. Fecal IgA concentrations tended to be greater in C10 than in CTRL, TM4, and TM10 calves, and in C4 and TM10 than in CTRL animals. Fecal propionate proportion was lesser in C10 than in CTRL, TM4, and TM10 calves, while butyrate was greater in C4 and C10 than in TM4 and CTRL calves. The proportion of non-normal fecal scores of C10 fed calves was greater than TM4 and TM10 calves. Results showed that TM and BC may help to recover intestinal functionality, provide gut immune protection, and increase liver fatty acid oxidation in calves after a FRF episode.

Heating Drinking Water in Cold Season Improves Growth Performance via Enhancing Antioxidant Capacity and Rumen Fermentation Function of Beef Cattle

The research aimed to investigate the suitable drinking water temperature in winter and its effect on the growth performance, antioxidant capacity, and rumen fermentation function of beef cattle. A total of 40 beef cattle (640 ± 19.2 kg) were randomly divided into five treatments with eight cattle in each treatment raised in one pen according to initial body weight. Each treatment differed only in the temperature of drinking water, including the room-temperature water and four different heat water groups named RTW, HW_1, HW_2, HW_3, and HW_4. The measured water temperatures were 4.39 ± 2.546 °C, 10.6 ± 1.29 °C, 18.6 ± 1.52 °C, 26.3 ± 1.70 °C, and 32.5 ± 2.62 °C, respectively. The average daily gain (ADG) showed a significant linear increase during d 0 to 60 and a quadratic increase during d 31 to 60 with rising water temperature (p < 0.05), and the highest ADG of 1.1911 kg/d was calculated at a water temperature of 23.98 °C (R2 = 0.898). The average rectal temperature on d 30 (p = 0.01) and neutral detergent fiber digestibility (p < 0.01) increased linearly with increasing water temperature. Additionally, HW_2 reduced serum triiodothyronine, thyroxine, and malondialdehyde (p < 0.05), and increased serum total antioxidant capacity (p < 0.05) compared with RTW. Compared with HW_2, RTW had unfavorable effects on ruminal propionate, total volatile fatty acids, and cellulase concentrations (p < 0.05), and lower relative mRNA expression levels of claudin-4 (p < 0.01), occludin (p = 0.02), and zonula occludens-1 (p = 0.01) in the ruminal epithelium. Furthermore, RTW had a higher abundance of Prevotella (p = 0.04), Succinivibrionaceae_UCG-002 (p = 0.03), and Lachnospiraceae_UCG-004 (p = 0.03), and a lower abundance of Bifidobacteriaceae (p < 0.01) and Marinilabiliaceae (p = 0.05) in rumen compared to HW_2. Taken together, heated drinking water in cold climates could positively impact the growth performance, nutrient digestibility, antioxidant capacity, and rumen fermentation function of beef cattle. The optimal water temperature for maximizing ADG was calculated to be 23.98 °C under our conditions. Ruminal propionate and its producing bacteria including Prevotella, Succinivibrionaceae, and Lachnospiraceae might be important regulators of rumen fermentation of beef cattle drinking RTW under cold conditions.

Metagenomic insights into the rumen epithelial integrity responses to the vitamin B1 supplement under high-concentrate diets treatments

Subacute ruminal acidosis (SARA) becomes the most common nutritional metabolic disease in high-yielding dairy cows and later fatting beef cattle because of the increasing consumption of high-concentrate diets in modern feeding patterns. Our previous research found a certain piece of evidence that adding 180 mg thiamine/kg DMI could increase the rumen pH and regulate the structure of the rumen microbial community in vivo. However, there is still limited experimental data on the effects of SARA on thiamine status, the damage to the structure of rumen epithelial cells, and the underlying mechanism of the epithelium alterations. For this purpose, a total of 18 Angus bulls (average 22.0-months-old) with an average live weight of 567.6 ± 27.4 kg were randomly allocated into a control treatment (CON), a high-concentrate diet treatment (HC), and a high-concentrate diet with the vitamin B1 supplement treatment (HCB). All bulls were conducted with a 7-day adjustment period followed by a 60-day-long main feeding procedure. Results indicated that ADFI and ADG significantly decreased in the HC treatment compared with CON (P < 0.05), while significantly increased after the VB1 supplement (P < 0.05). Besides, ruminal acetate content was significantly downregulated while propionate was significantly upregulated under the HC treatment compared with CON (P < 0.05); however, these alterations showed a completely inverse regulatory effect on the VB1 supplement compared with HC (P < 0.05). These changes causatively induced a significant decrease in the A/P ratio in the HC treatment compared with CON and HCB treatments (P < 0.05). Bacterial communities in the HC treatment could be separated from those in CON through PCoA axes 1 and 2. Meanwhile, the VB1 supplement significantly altered the bacterial communities compared with the HC treatment, except for HCB-3. Furthermore, the HC treatment significantly upregulated the expression of JNK, Bax, Caspase-8, Caspase-3, Caspase-9, and Cyt-C compared with CON, while significantly downregulated the expression of Bcl-2. The VB1 supplement showed a complete converse gene expression compared with HC. In conclusion, the VB1 supplement could effectively attenuate the alterations that occurred when exposed to high-concentrate diets, and help promote production performance through increased fermentability.

Elliptical and linear relationships with rumen temperature support a homeorhetic trajectory for DMI during recovery of feedlot cattle exposed to moderate heat load

Most feedlot animals in Australia experience 2 to 3 moderate heat waves during summer. This study aimed to gain understanding of the physiological drivers in response to and during recovery from such events with a view to designing strategies to ensure rapid and safe recovery. Two hypotheses were tested during thermal challenge and recovery in climate-controlled rooms (CCR): firstly, the feedlot steer on a grain-based diet mounts appropriate physiological responses during moderate heat load and in recovery so that its performance and physiology state after recovery is not different to the feed restricted thermoneutral (FRTN) steer. Secondly, commonly used indicators of increased heat load, e.g., respiration rate (RR), panting score (PS), body surface temperatures (ST), and water consumption (WC), reflect rumen temperature (RT) during thermal challenge and recovery at the level of daily means. In this study, 36 Angus steers (live weight (LW) 451.5 ± 22.6 kg) made up 3 cohorts of 12 animals that sequentially underwent the CCR phase. For this 18-d phase, the steers were allocated to either a moderate heat load treatment (thermally challenged, TC, n = 18) or a FRTN treatment (n = 18). The TC group underwent 3 periods, Pre-Challenge (4 d, temperature humidity index (THI) range of 68 to 71), Challenge (7 d, THI 73 to 84 with diurnal cycling), and Recovery (7 d, THI 68 to 71). The FRTN group were held at thermoneutral conditions in the CCR (THI 66.9 ± 0.3), and each animal was offered an amount of feed was based on the feed intake of its LW matched TC pair. Thus, as DMI fell in the TC group during Challenge, feed restriction was imposed on the FRTN group. The data were collected by trained observers were DMI, RT, RR, PS, body STs (forehead, shoulder, leg, rump), and WC. Challenge induced a heat stress response in the TC group with reduced DMI and LW, and elevated RT, RR, PS, body STs, and WC (P < 0.001). These measures were unchanged or reduced in the FRTN group (P < 0.001). At the end of Recovery, the TC and FRTN groups had converged on most measures including LW. Daily mean RT of both groups showed strong linear relationships with THI, RR, PS, head ST, and WC (P ≤ 0.0022) but opposing elliptical relationships with DMI; that is, as DMI fell with increasing RT for the TC group, DMI increased with rising RT for the FRTN group. In all, the feedlot steers in this study demonstrated sufficient homeorhetic capacity to adjust to moderate heat load and recover from it.

The impacts of a fibrolytic enzyme additive on digestibility and performance in the grower and early finisher period, and supplemental Saccharomyces cerevisiae on performance and rumen health in the late finisher period for feedlot cattle

Two experiments were conducted to determine the effects of a fibrolytic enzyme pretreatment on growth performance, apparent total tract digestibility, and ruminal pH throughout the grower and early finisher period (exp. 1), and to examine the impact of Saccharomyces cerevisiae supplementation on intake, performance, and indicators of gut health in the late finisher period (exp. 2). A total of 54 steers were randomly assigned to a subgroup determining experimental treatment groups. In exp. 1, steers were randomized to control (CON1; no enzyme) or enzyme [ENZ; 0.75 mL·kg−1 dry matter (DM) of feed] dietary treatments. Digestibility was improved (P ≤ 0.05) in ENZ steers for DM, crude protein, net energy for gain, and sugars but did not affect (P ≥ 0.12) dry matter intake (DMI), average daily gain (ADG), or reticulo-ruminal pH. In exp. 2, the treatments were control (CON2; no yeast) or yeast (YST; 3.0 g·animal−1 daily) supplemented diets. Rumen papillae were collected for mRNA expression of gut barrier function (OCLN, CLDN, ZO1, and ZO2) and immune response (TLR2, TLR4, and FCAR) genes and histological measurements. Yeast supplementation decreased (P < 0.001) DMI by 31%, reduced variation in DMI, and improved feed conversion ratios but did not impact rumen health mRNA expression or histology measures (P ≥ 0.07). Overall, enzyme supplementation improved the digestibility of some nutrients in the grower period, and yeast supplementation improved feed efficiency, without impacting growth performance or gut health.

Effects of conditioning, source, and rest on indicators of stress in beef cattle transported by road

Consumers are increasingly concerned about the welfare of farm animals, especially during transportation. The Canadian transport regulations state that weaned cattle require an 8 h rest after 36 h of transport. There are, however, only a few studies that assess the effect of rest on the welfare of beef cattle. The aim of this study was to assess the effect of conditioning, source and rest on indicators of welfare in 7-8-month-old beef calves during long-distance transport. Treatments consisted of a 2 × 2 × 2 factorial design where the main factors were conditioning: conditioned (C; n = 160) or non-conditioned (N; n = 160); source: auction market (A; n = 160) or ranch direct (R; n = 160); and rest: 0 h (0 h; n = 160) or 8 h (8 h; n = 160). Means of non-esterified fatty acids (NEFA), serum amyloid-A, haptoglobin, creatine kinase (CK), and percentage of time standing from N calves were greater than C calves (all p ≤ 0.05). Means of percentage of time standing and CK of R calves were greater than A calves (both p ≤ 0.05). The mean of NEFA of 0 h calves was greater than the 8 h calves (p < 0.01), while the percentage of time standing of 0 h calves was less than 8 h calves (p < 0.01). Statistically significant differences between means of NEFA and standing percentage, were observed between 0 h and 8h calves. Few and inconsistent indicators of reduced welfare were observed between auction market and ranch direct calves, while non-conditioning was associated with greater physiological and behavioural indicators of reduced welfare. Based on these results, conditioning should be implemented as a management practice to improve the welfare of transported calves.

Interactions Between Rumen Microbes, VFAs, and Host Genes Regulate Nutrient Absorption and Epithelial Barrier Function During Cold Season Nutritional Stress in Tibetan Sheep

As one of the important ruminants of the Qinghai-Tibet Plateau, Tibetan sheep are able to reproduce and maintain their population in this harsh environment of extreme cold and low oxygen. However, the adaptive mechanism of Tibetan sheep when nutrients are scarce in the cold season of the Plateau environment is unclear. We conducted comparative analysis rumen fermentation parameters, rumen microbes, and expression of host genes related to nutrient absorption and rumen epithelial barrier function in cold and warm season Tibetan sheep. We found that concentrations of the volatile fatty acids (VFAs) acetate, propionate and butyrate of Tibetan sheep in the cold season were significantly higher than in the warm season (P < 0.05). Microbial 16S rRNA gene analysis revealed significant differences in rumen microbiota between the cold and warm seasons, and the abundance of microbial in the cold season was significantly higher than that in the warm season (P < 0.05), and the lack of nutrients in the cold season led to a significant reduction in the expression of SGLT1, Claudin-4, and ZO-1 genes in the rumen epithelium. Correlation analysis revealed significant associations of some rumen microorganisms with the fermentation product acetate and the rumen epithelial genes SGLT1, Claudin-4, and ZO-1.

Flooding on Beef and Swine Farms: A Scoping Review of Effects in the Midwestern United States

BACKGROUND

Increasing uncertainty and variability in weather due to climate change puts enormous stress on the sustainability of agricultural communities in several parts of the continental United States. Rural agriculture-based communities, such as those in North Carolina, Nebraska, and Illinois are particularly vulnerable to the impacts of flooding. These extreme weather events affect many animal facilities, and flooding can cause long-term impacts on animal health and productivity.

OBJECTIVES

This scoping review investigated the potential short- and long-term ramifications of flooding on beef cattle and swine farms with theoretical locations in the Midwestern U.S. The goal of this review is to create a concept map to identify research gaps related to efforts to support those animals and peoples ravaged by floods. This was accomplished by performing a scoping review using search terms "beef OR swine AND flood" to assess direct effects and then "beef OR swine AND direct effect" to evaluate secondary and tertiary effects.

RESULTS

Our findings were based on a total of 89 peer-reviewed publications, with 50 publications relating to beef cattle, 24 relating to swine, and 15 containing information applicable to both. On beef farms, the effects of flooding can be broad and long-lasting. The short-term risks of flooding are reasonably well-understood, including the comingling of unfamiliar cattle, nutritional restriction, and disease transmission. However, long-term impacts, including potential effects on reproduction, nutrition, and carcass quality, have been less studied. In particular, further research is needed on mold species that contaminate hay post-flood, the effect of moldy hay ingestion on cattle, and the effects of heavy metal consumption on cattle and consumers. Little research is available regarding the effects of flooding on swine farms, likely due to the highly intensive nature of swine operations. In general, swine farms suffer from acute infectious diseases and biosecurity risks after flooding events.

CONCLUSIONS

The potential ramifications of flooding on livestock farms differ among farm operations. Beef farms should prepare for long-term impacts on nutrition and reproduction, while swine farms should prepare for short-term impacts on biosecurity.

Effects of short-term fasting on ruminal pH and volatile fatty acids in cattle fed high-roughage versus high-concentrate diets

We evaluated whether the dietary roughage-to-concentrate ratio affects ruminal pH and volatile fatty acids (VFAs) in response to a one-time morning fast. Four healthy rumen-cannulated Holstein steers 4–5 months old were used. Cattle were subjected to 2 weeks of adaptation (high-roughage or high-concentrate diet), and morning feed restriction was performed on the day after the adaptation period ended (Day 0). Thereafter, each diet was reintroduced on the evening of Day 0. Our results showed that the 1-hr mean ruminal pH from 0800 to 1900 on Day 0 was higher, and that from 1700 to 1900 on Day 1 was lower (P<0.05) than pH on 1 day before fasting (Day −1) in cattle fed both diets. On Day 0, total VFA levels decreased after morning fasting and were lower (P<0.05) than those on Day −1 irrespective of evening refeeding. Furthermore, blood non-esterified fatty acid and beta-hydroxybutyric acid levels on Day 0 increased and decreased, respectively, compared to Day −1 in cattle fed both diets. These results indicate that even a one-time feed restriction can disrupt ruminal fermentation, and the changes can persist to the next day after fasting.

Health and production effects of killed vaccines against Mannheimia haemolytica, bovine viral diarrhoea virus and bovine herpesvirus 1, in locally backgrounded feedlot cattle

OBJECTIVES

This study evaluates the effects of respiratory vaccines on health and growth rates in cattle placed in local backgrounding facilities then feedlots.

METHODS

A total of 7011 cattle entering backgrounding facilities contiguous with six feedlots in Australia were allocated to eight respiratory vaccine categories, including an untreated control category. The vaccines, against Mannheimia haemolytica, bovine viral diarrhoea virus and bovine herpesvirus 1, were administered in various combinations at backgrounding facility entry and subsequent feedlot entry. Cattle were held in the backgrounding facilities for a minimum of 28 days.

RESULTS

During their feedlot phase, 3.7% of study animals were detected with bovine respiratory disease (BRD). BRD sub hazard was lowest in cattle vaccinated with Bovilis MH + infectious bovine rhinotracheitis® (sub hazards ratio: 0.47; 95% confidence interval: 0.27-0.83; P = 0.010), and point estimates for other vaccine combinations did not differ (P > 0.10) from controls. Six of the respiratory vaccine combinations decreased growth rate during backgrounding relative to untreated controls (P ≤ 0.003). Overall, the feedlot growth rate was not significantly affected by the vaccine category (overall Wald P = 0.191).

CONCLUSIONS

Use of these respiratory vaccines in cattle held for at least 28 days in backgrounding facilities contiguous with their feedlots before feedlot entry reduces growth rate during the backgrounding period and does not result in large beneficial effects on either BRD risk or average daily live weight gain during the feedlot phase.

Feeding colostrum or a 1:1 colostrum:milk mixture for 3 days postnatal increases small intestinal development and minimally influences plasma glucagon-like peptide-2 and serum insulin-like growth factor-1 concentrations in Holstein bull calves

This study evaluated how feeding colostrum- or a colostrum-milk mixture for 3 d postnatal affects plasma glucagon-like peptide-2 (GLP-2), serum insulin-like growth factor-1 (IGF-1), and small intestinal histomorphology in calves. Holstein bulls (n = 24) were fed colostrum at 2 h postnatal and randomly assigned to receive either colostrum (COL), whole milk (WM), or a 1:1 COL:WM mixture (MIX) every 12 h from 12 to 72 h. A jugular venous catheter was placed at 1 h postnatal to sample blood frequently for the duration of the experiment. Samples were collected at 1, 2, 3, 6, 9, 11, and 12 h. Following the 12-h meal, blood was collected at half-hour intervals until 16 h and then at 1-h intervals from 16 to 24 h. A 27-h sample was taken, then blood was sampled every 6 h from 30 to 60 h. Again, blood was taken at half-intervals from 60 to 64 h, then at 65 and 66 h, following which, a 2-h sampling interval was used until 72 h. Plasma GLP-2 (all time points) and serum IGF-1 (at time points: 1, 6, 12, 18, 24, 36, 48, and 72 h) were both analyzed. Duodenal, jejunal, and ileal tissues were collected at 75 h of age to assess histomorphology and cellular proliferation. Feeding COL, rather than WM, increased plasma GLP-2 by 60% for 2 h and tended to increase GLP-2 by 49.4% for 4 h after the 60-h meal. Insulin-like growth factor-1 area under the curve (from 12 to 72 h) tended to be 27% greater for COL than WM calves but was otherwise unaffected by treatment. Ileal crypts tended to proliferate more with MIX than WM, whereas ileal crypt proliferation did not differ for COL compared with MIX or WM and was not different between treatments in the proximal jejunum. Villi height was increased 1.8 and 1.5× (COL and MIX vs. WM) in the proximal and distal jejunum, respectively, whereas MIX duodenal and ileal villi height tended to be 1.5 and 1.4× that of WM. Crypt depth did not differ in any region. Surface area of the gastrointestinal tract was reduced for WM by 60 and 58% (proximal jejunum) and 38 and 52% (ileum) relative to COL and MIX and was 54% less than MIX in the distal jejunum. Overall, extended COL feeding minimally increased plasma GLP-2 and serum IGF-1 compared with WM feeding. As COL and MIX similarly promoted small intestinal maturation, feeding calves transition milk to promote intestinal development could be a strategy for producers.

The influence of Megasphaera elsdenii on rumen morphometrics of cull cows immediately stepped up to a high-energy finishing diet

Forty-five beef cull cows [body weight (BW) = 503 ± 58 kg; body condition score (BCS) = 2.1 ± 0.6] were randomized into two treatments to compare the effects of oral drenching of no probiotic vs. 100 mL of Megasphaera elsdenii NCIMB 41125 (M. elsdenii culture; Lactipro Advance; 2 × 10⁸ cfu/mL; MS Biotec, Inc., Wamego, KS) on the realimentation of cull cows. The study featured a rapid 0-d step-up of concentrate-naïve cull cows to a 90% concentrate diet (1.43 Mcal/kg of NE_g). The cows were finished for 35 d and were fitted with a wireless rumination tag (Allflex Flex Tag; SCR Engineers, Ltd, Netanya, Israel), which tracked head movement to record eating and chewing activity. Rumen morphometrics was recorded on the harvest floor, with each carcass assigned a rumenitis score, and a fragment of the cranial sac removed for further papillae analysis. An additional 23, thin, non-fed cull cows were harvested at the same abattoir to compare the effects of concentrate realimentation on ruminal morphometrics. Megasphaera elsdenii culture-drenched cattle registered a 13.3% increase in rumination time (39.27 min/d, P = 0.03) during the first week of the trial compared to controls. A numerical rumination advantage for M. elsdenii culture-administered cattle was observed during week 2 of trial (P = 0.17), with no differences between treatments from weeks 3 to 5 (P ≥ 0.40). Subjective rumenitis evaluations approached a tendency (P = 0.12), with non-M. elsdenii culture-drenched concentrate-fed cattle logging twice the score of their day 0 cohorts (2.52 vs. 1.17) suggesting considerable lactic insults occurred to the ruminal epithelium in the short 35-d trial. Despite the short feeding duration, concentrate realimentation prompted a significant improvement in mean papillae area (P < 0.01). Among concentrate-fed treatments, M. elsdenii culture-drenched cattle posted superior absorptive surface area (P = 0.01) and a greater ratio of papillae area of absorptive surface area (P = 0.05), suggesting that M. elsdenii culture is favorably altering the ecology of the rumen and promoting papillae growth perhaps by mitigating lactate-driven pH drops. In conclusion, M. elsdenii culture application in a 0-d step-up protocol to finishing diets can help mitigate the effects of ruminal acidosis.

The Use of Biochemical Measurements to Identify Pre-Slaughter Stress in Pasture Finished Beef Cattle

This study considered the relationship between pre-slaughter stressors and plasma biomarkers in 488 pasture-raised cattle across two experiments. The design aimed to test groups consisting of steer only, heifer only, and mixed sex cattle under direct kill versus rested (14 days in abattoir holding paddocks) protocols. In Experiment One, cattle were sourced from four farms, and transported by trucks and ships on the same day. In Experiment Two, cattle were sourced from four farms where a comparison was made between marketing via two commercial saleyards or direct farm gate consignment to abattoir. Blood samples were collected at exsanguination for subsequent analyses and relation to meat quality attributes. Muscle damage, as indicated by creatine kinase, is the biomarker most correlated to ultimate pH and muscle glycogen concentrations. A two-week rest period is effective for lowering this enzyme and improving muscle glycogen concentration. Although the cattle was subjected to a range of stress inducing treatments, we found that plasma biomarkers alone appeared insufficient for use as diagnostic stress indicators.

Adaptive responses in short-chain fatty acid absorption, gene expression, and bacterial community of the bovine rumen epithelium recovered from a continuous or transient high-grain feeding

The feeding of high-grain diets to dairy cows commonly results in lowered pH and ruminal dysbiosis, characterized by changes in absorption dynamics of short-chain fatty acids (SCFA) across the reticuloruminal wall, epithelial function, and the epithelial bacteria community structure. Therefore, the present study evaluated the effect of high-grain feeding persistence on the absorption kinetics of reticuloruminal SCFA, gene expression in the rumen epithelium, and the associated shifts in the epithelial bacteria in cows recovering from either a long-term continuous high-grain feeding model or a long-term transient high-grain feeding model. In a crossover study design, 8 nonlactating Holstein cows were fed 60% concentrate either continuously for 4 wk (continuous) or with a 1-wk break in the second week of the high-grain feeding (transient). After the high-grain feeding, all animals were fed a diet of 100% forage (recovery) for an additional 8 wk. Rumen papilla biopsies and SCFA absorption measurements were taken at the start of the trial (baseline), after the 4-wk high-grain feeding (49 d), after 2-wk recovery forage feeding (63 d), and after 8-wk recovery forage (105 d). Absorption of SCFA was determined in vivo using the washed and isolated reticulorumen technique. Rumen papillae biopsies were used for adherent bacterial DNA and host RNA extraction. The epithelial bacteria were determined using Illumina MiSeq (Microsynth AG, Balgach, Switzerland) sequencing of the 16S rRNA gene. No significant effects of the high-grain feeding model were seen for bacterial diversity. However, bacterial diversity increased with time spent in the recovery forage feeding period regardless of feeding model. The relative abundance of Acidobacteria phyla and Acetivibrio spp. increased when animals were fed a transient high-grain feeding model. A trend toward increased CLDN4 expression was observed in the continuous model. Furthermore, there were interactions between feeding model and sampling day for gene targets CD14, DRA, NHE2, NHE3, and MCT2. When comparing length of recovery, in the continuous model increased relative absorption of SCFA was sustained at 63 d but dropped to baseline measurements at 105 d. A similar pattern was found with the transient model but it did not reach significance. The only gene target that was found to significantly correlate to relative absorption of SCFA was DRA (correlation coefficient ≤ -0.41). Whereas, genera Alkalibaculum, Anaerorhabdus, Coprococcus, and Dethiobacter all showed positive correlations to gene targets for pH regulation (NHE2 and NHE3) and SCFA uptake (MCT1) but negative correlations to SCFA absorption. We conclude that while the rumen absorption and epithelial bacteria were able to recover to baseline levels after 8 wk of forage feeding, the time needed for re-establishment of homeostasis in host gene expression is longer, especially when high-grain feeding is interrupted.

Impact of 24-h feed, water, or feed and water deprivation on feed intake, metabolic, and inflammatory responses in beef heifers

This experiment investigated the effects of 24-h feed or water deprivation on hay intake, metabolic, and inflammatory responses in growing beef heifers. Forty Angus × Hereford heifers were ranked by initial BW (275 ± 6 kg) and age (278 ± 6 d) and randomly allocated to 20 drylot pens (2 heifers/pen). Pens were randomly assigned to 1 of 5 squares (4 × 4; 4 pens/square; a total of 8 animals per square), that were run simultaneously with each containing 4 experimental periods of 17 d each (day -6 to 10). From day -5 to 0 of each period, pens were offered alfalfa-grass hay ad libitum + 454 g of dried distillers grains with solubles (as-fed basis) per heifer daily. On day 0 of each period, pens received 1 of 4 treatments: 1) feed and water deprivation for 24 h (FWD), 2) feed deprivation for 24 h, but regular access to water (FD), 3) water deprivation for 24 h, but regular access to feed (WD), or 4) regular access to feed and water (CON). Treatments were concurrently applied from day 0 to 1. Heifer full BW was collected on day -6 and -5, before (day 0) and after (day 1) treatment application, and on day 3, 6, 9, and 10 of each period. Hay DMI was recorded daily from day -5 to 10. Blood samples were collected on day -5, 0, 1, 3, 6, and 10 of each experimental period. Following treatment application on day 1, BW loss was greater, and BW was less (P < 0.01) in WD, FWD, and FD compared with CON heifers, and similar (P = 0.64) among FWD and FD heifers. No treatment effects were detected (P ≥ 0.21) for final BW and overall ADG. Plasma cortisol concentrations were greater (P < 0.01) in FD and FWD vs. WD and CON on day 1, whereas FD had greater (P < 0.01) plasma cortisol concentration vs. CON, WD, and FWD on day 6 and 10. Serum NEFA concentration was greater (P < 0.01) in FD and FWD vs. WD and CON on day 1, and greater (P < 0.01) in WD vs. CON heifers on day 1. No treatment effects were detected (P = 0.53) for plasma haptoglobin concentration. Plasma ceruloplasmin concentration was greater (P < 0.01) in FD and FWD vs. CON on day 1, and greater (P < 0.01) in FD vs. CON and WD on day 3 and 6. Collectively, feed or water deprivation for 24 h did not impact feed intake and BW gain, whereas metabolic results suggest that feed deprivation stimulates cortisol, NEFA, and ceruloplasmin responses in growing beef heifers.

Oversupplying metabolizable protein in late gestation for beef cattle: effects on postpartum ruminal fermentation, blood metabolites, skeletal muscle catabolism, colostrum composition, milk yield and composition, and calf growth performance

The objective of the study was to determine whether oversupplying MP prepartum affects postpartum cow BW, colostrum composition, milk production and composition, protein catabolism in the dam, and calf growth. Crossbred Hereford heifers were individually fed a control treatment designed to meet MP requirements (CON; n = 10) or 133% of the MP requirement (HMP; n = 11) from day -55 ± 4 until parturition. All cows were provided a common postpartum diet. Cow BW was measured on days 7 ± 1, 14 ± 2, 28 ± 3, 57 ± 4, 82 ± 5, and 111 ± 3 relative to parturition. DMI and ruminal pH were measured daily and summarized by week until day 33. Milk yield was estimated based on a 12-h two-quarter milk yield on days 7 ± 1, 12 ± 1, 28 ± 3, 33 ± 3, 70 ± 3, and 112 ± 3. Urine samples were collected from cows over a 6-d period starting on days 7 ± 1 and 28 ± 3 and the composited samples were analyzed for 3-methylhistidine (3-MH) and creatinine. Muscle samples were collected from cows on day 13 ± 1 while calf muscle samples were collected on days 2 and 111 ± 3 of age. Muscle samples from cows were analyzed for markers of protein catabolism, and calf muscle samples were analyzed for genes regulating cell growth and differentiation. Data were analyzed as a randomized complete block design using the MIXED procedure of SAS accounting for repeated measures when necessary. Postpartum BW did not differ (P ≥ 0.30) by treatment, day, or the interaction of treatment and day (T × D), but rump fat decreased (P = 0.011) as lactation progressed. DMI decreased during weeks 2 and 3 compared to 1 and 4, whereas ruminal pH was less during weeks 2, 3, and 4 relative to week 1. Colostrum fat concentration was less (P = 0.003) for HMP than CON; but, milk production was not affected by treatment. Milk yield was greatest from days 7 to 33 and decreased thereafter (P < 0.01). Urinary 3-MH and the 3-MH:creatinine ratio did not differ by treatment, day, or the T × D (P ≥ 0.22) interaction, nor was there a difference (P ≥ 0.13) in the abundance of catabolic proteins. Calf growth was not affected by treatment, but HMP calves had greater expression (T × D, P = 0.05) of PPARG while PKM expression increased for CON calves (T × D, P = 0.04) at day 111 compared to their expression at day 2. Overfeeding MP during late gestation does not improve postpartum indicators of N balance or maternal muscle turnover but may alter colostrum composition and calf gene expression at weaning.

Effect of ruminal acidosis and short-term low feed intake on indicators of gastrointestinal barrier function in Holstein steers

The objective of this study was to determine effect of ruminal acidosis (RA) and low feed intake [LFI] on the regional barrier function of the gastrointestinal tract. Twenty-one Holstein steers were fed for ad libitum intake for 5 d (control [CON]), fed at 25% of ad libitum intake for 5 d (LFI), or provided 2 d of ad libitum intake followed by 1-d of feed restriction (25% of ad libitum intake), 1 d where 30% of ad libitum dry matter intake (DMI) was provided as pelleted barley followed by the full allocation (RA) and fed for ad libitum intake the following day. Tissues and digesta from the rumen, omasum, duodenum, jejunum, ileum, cecum, proximal, and distal colon were collected. Permeability was assessed using the mucosal-to-serosal flux of inulin (JMS-inulin) and mannitol (JMS-mannitol). Digesta pH was 0.81, 0.63, and 0.42 pH units less for RA than CON in the rumen, cecum, and proximal colon; while, LFI had pH that was 0.47 and 0.36 pH units greater in the rumen and proximal colon compared to CON. Total ruminal short-chain fatty acid (SCFA) concentration were less for LFI (92 mM; P = 0.010) and RA (87 mM; P = 0.007) than CON (172 mM) steers. In the proximal colon, the proportion of butyrate (P = 0.025 and P = 0.022) and isobutyrate (P = 0.019 and P = 0.019) were greater, and acetate (P = 0.028 and P = 0.028) was less for LFI and RA, respectively, when compared to CON steers. Ruminal papillae length, width, perimeter, and surface area were 1.21 mm, 0.78 mm, 3.84 mm, and 11.15 mm2 less for LFI than CON; while, RA decreased papillae width by 0.52 mm relative to CON. The JMS-mannitol was less for LFI steers than CON in the proximal colon (P = 0.041) and in the distal colon (P = 0.015). Increased gene expression for claudin 1, occludin, tight-cell junction protein 1 and 2, and toll-like receptor 4 were detected for LFI relative to CON in the rumen, jejunum, and proximal colon. For RA steers, expression of toll-like receptor 4 in the rumen, and occludin and tight-cell junction protein 1 were greater in the jejunum than CON. An acute RA challenge decreased pH in the rumen and large intestine but did not increase tissue permeability due to increases in the expression of genes related to barrier function within 1 d of the challenge. Steers exposed to LFI for 5 d had reduced ruminal SCFA concentrations, smaller ruminal papillae dimensions, and increased tissue permeability in the proximal and distal colon despite increases for genes related to barrier function and immune function.

Evidence of In Vivo Absorption of Lactate and Modulation of Short Chain Fatty Acid Absorption from the Reticulorumen of Non-Lactating Cattle Fed High Concentrate Diets

Short-chain fatty acids (SCFAs) and lactate are endproducts of rumen fermentation and important energy sources for the host ruminant. Because their rapid accumulation results in ruminal acidosis, enhancement of the absorption of SCFA and lactate across reticuloruminal wall is instrumental in increasing energy supply and preventing ruminal acidosis in cattle. This study investigated whether the reticuloruminal absorption of SCFAs and lactate was altered by different strategies of high concentrate feeding. Eight rumen-cannulated, non-lactating Holstein cows were fed a forage-only diet (baseline) and then gradually adapted over 6 d to a 60% concentrate level. Thereafter, this concentrate-rich diet was fed for 4 wk either continuously (Con; n = 8) or interruptedly (Int; n = 8). Absorption of SCFAs and lactate was determined in vivo from the experimental buffer introduced into the washed reticulorumen. The buffer contained acetate, propionate, butyrate and lactate at a concentration of 60, 30, 10 and 5 mmol/L, respectively and Cr-EDTA as a marker for correcting ruminal water fluxes. The reticuloruminal absorption after 35 and 65 min of buffer incubation was measured at the baseline, after 1 wk of 60% concentrate feeding in the interrupted model (Int-1) and after 4 wk of concentrate feeding in both feeding models (Int-4 and Con-4). Data showed that the absorption rates of individual and total SCFAs during the first 35 min of incubation of Con-4 were highest (~1.7 times compared to baseline), while Int-1 and Int-4 were similar to respective baseline. Lactate was not absorbed during forage-only baseline and 1-wk concentrate feeding, but after 4-wk feeding of concentrates in both models. In conclusion, SCFAs absorption across the reticulorumen of non-lactating cattle was enhanced by the 4-wk continuous concentrate feeding, which seems to be more advantageous in terms of rumen acidosis prevention compared to the interrupted feeding model. The study provides evidence of lactate absorption across the reticulorumen of non-lactating cattle after both continuous and interrupted 4-wk concentrate feeding.

Examination of the molecular control of ruminal epithelial function in response to dietary restriction and subsequent compensatory growth in cattle

BACKGROUND

The objective of this study was to investigate the effect of dietary restriction and subsequent compensatory growth on the relative expression of genes involved in volatile fatty acid transport, metabolism and cell proliferation in ruminal epithelial tissue of beef cattle. Sixty Holstein Friesian bulls (mean liveweight 370 ± 35 kg; mean age 479 ± 15 d) were assigned to one of two groups: (i) restricted feed allowance (RES; n = 30) for 125 d (Period 1) followed by ad libitum access to feed for 55 d (Period 2) or (ii) ad libitum access to feed throughout (ADLIB; n = 30). Target growth rate for RES was 0.6 kg/d during Period 1. At the end of each dietary period, 15 animals from each treatment group were slaughtered and ruminal epithelial tissue and liquid digesta harvested from the ventral sac of the rumen. Real-time qPCR was used to quantify mRNA transcripts of 26 genes associated with ruminal epithelial function. Volatile fatty acid analysis of rumen fluid from individual animals was conducted using gas chromatography.

RESULTS

Diet × period interactions were evident for genes involved in ketogenesis (BDH2, P = 0.017), pyruvate metabolism (LDHa, P = 0.048; PDHA1, P = 0.015) and cellular transport and structure (DSG1, P = 0.019; CACT, P = 0.027). Ruminal concentrations of propionic acid (P = 0.018) and n-valeric acid (P = 0.029) were lower in RES animals, compared with ADLIB, throughout the experiment. There was also a strong tendency (P = 0.064) toward a diet × period interaction for n-butyric with higher concentrations in RES animals, compared with ADLIB, during Period 1.

CONCLUSIONS

These data suggest that following nutrient restriction, the structural integrity of the rumen wall is compromised and there is upregulation of genes involved in the production of ketone bodies and breakdown of pyruvate for cellular energy. These results provide an insight into the potential molecular mechanisms regulating ruminal epithelial absorptive metabolism and growth following nutrient restriction and subsequent compensatory growth.

Ruminal pH predictions for beef cattle: Comparative evaluation of current models

This study evaluated 8 empirical models for their ability to accurately predict mean ruminal pH in beef cattle fed a wide range of diets. Models tested that use physically effective fiber (peNDF) as a dependent variable were Pitt et al. (1996, PIT), Mertens (1997, MER), Fox et al. (2004, FOX), Zebeli et al. (2006, ZB6), and Zebeli et al. (2008, ZB8), and those that use rumen VFA were Tamminga and Van Vuuren (1988, TAM), Lescoat and Sauvant (1995, LES), and Allen (1997, ALL). A data set of 65 published papers (231 treatment means) for beef cattle was assembled that included information on animal characteristics, diet composition, and ruminal fermentation and mean pH. Model evaluations were based on mean square prediction error (MSPE), concordance correlation coefficient (CCC), and regression analysis. The prediction potential of the models varied with low root MSPE (RMSPE) values of 4.94% and 5.37% for PIT and FOX, RMSPE values of 9.66% and 12.55% for ZB6 and MER, and intermediate RMSPE values of 5.66% to 6.26% for the other models. For PIT and FOX, with the lowest RMSPE, approximately 96% of MSPE was due to random error, whereas for ZB6 and MER, with the highest RMSPE, 15.85% and 23.42% of MSPE, respectively, was due to linear bias, and 37.19% and 60.12% of the error, respectively, was due to deviation of the regression slope from unity. The CCC was greatest for PIT (0.67) and FOX (0.62), followed by 0.60 for LES and TAM, 0.52 for ZB8, 0.39 for MER, 0.34 for ALL, and 0.22 for ZB6. Residuals plotted against model-predicted values showed linear bias (P < 0.001) for all models except PIT (P = 0.976) and FOX (P = 0.054) and mean bias (P < 0.001) except for FOX (P = 0.293), LES (P = 0.215), and TAM (P = 0.119). The study showed that the empirical models PIT and FOX, based on peNDF, and LES and TAM, based on VFA, are preferred over the others for prediction of mean ruminal pH in beef cattle fed a wide range of diets. Several animal (BW and intake), diet (forage and OM contents), and ruminal (ammonia and acetate concentrations) factors were (P < 0.001) related to the residuals for each model. We conclude that the accuracy of prediction of mean ruminal pH was relatively low for all extant models. Consideration of factors in addition to peNDF and total VFA, as well as the use of data from studies with continuous measurement of ruminal pH over 24 h or more, would be useful in the development of improved models for predicting ruminal pH in beef cattle.

Illumina MiSeq Phylogenetic Amplicon Sequencing Shows a Large Reduction of an Uncharacterised Succinivibrionaceae and an Increase of the Methanobrevibacter gottschalkii Clade in Feed Restricted Cattle

Periodic feed restriction is used in cattle production to reduce feed costs. When normal feed levels are resumed, cattle catch up to a normal weight by an acceleration of normal growth rate, known as compensatory growth, which is not yet fully understood. Illumina Miseq Phylogenetic marker amplicon sequencing of DNA extracted from rumen contents of 55 bulls showed that restriction of feed (70% concentrate, 30% grass silage) for 125 days, to levels that caused a 60% reduction of growth rate, resulted in a large increase of relative abundance of Methanobrevibacter gottschalkii clade (designated as OTU-M7), and a large reduction of an uncharacterised Succinivibrionaceae species (designated as OTU-S3004). There was a strong negative Spearman correlation (ρ = -0.72, P = <1x10^-20) between relative abundances of OTU-3004 and OTU-M7 in the liquid rumen fraction. There was also a significant increase in acetate:propionate ratio (A:P) in feed restricted animals that showed a negative Spearman correlation (ρ = -0.69, P = <1x10^-20) with the relative abundance of OTU-S3004 in the rumen liquid fraction but not the solid fraction, and a strong positive Spearman correlation with OTU-M7 in the rumen liquid (ρ = 0.74, P = <1x10^-20) and solid (ρ = 0.69, P = <1x10^-20) fractions. Reduced A:P ratios in the rumen are associated with increased feed efficiency and reduced production of methane which has a global warming potential (GWP 100 years) of 28. Succinivibrionaceae growth in the rumen was previously suggested to reduce methane emissions as some members of this family utilise hydrogen, which is also utilised by methanogens for methanogenesis, to generate succinate which is converted to propionate. Relative abundance of OTU-S3004 showed a positive Spearman correlation with propionate (ρ = 0.41, P = <0.01) but not acetate in the liquid rumen fraction.

The duration of time that beef cattle are fed a high-grain diet affects the recovery from a bout of ruminal acidosis: dry matter intake and ruminal fermentation

This study was conducted to determine if the duration of time cattle are fed a high-grain diet affects their susceptibility to and recovery from ruminal acidosis. Sixteen Angus heifers (BW ± SEM, 261 ± 6.1 kg) were assigned to 1 of 4 blocks and fed a backgrounding diet consisting of 60% barley silage, 30% barley grain, and 10% supplement (DM basis). Within block, cattle were randomly assigned to 1 of 2 treatments differing in the number of days they were fed the high-grain diet before an acidosis challenge: 34 d for long adapted (LA) and 8 d for short adapted (SA). All heifers were exposed to the same 20 d dietary transition to a high-grain diet containing 9% barley silage, 81% barley grain, and 10% supplement (DM basis). Ruminal acidosis was induced by restricting feed to 50% of DMI:BW for 24 h followed by an intraruminal infusion of ground barley at 10% DMI:BW. Heifers were then given their regular diet allocation 1 h after the intraruminal infusion. Data were collected during an 8-d baseline period (BASE), on the day of the acidosis challenge (CHAL), and during 2 consecutive 8-d recovery periods (REC1 and REC2). Acidosis induction increased daily duration (531 to 1,020 min/d; P < 0.001) and area (176 to 595 (min × pH)/d; P < 0.001) that ruminal pH was <5.5 relative to BASE. Relative to BASE, inducing acidosis also increased the daily mean (0.3 to 11.4 mM; P = 0.013) and maximum (1.3 to 29.3 mM; P = 0.008) ruminal fluid lactate concentrations. There was no effect of dietary treatment on ruminal pH, lactate, or short-chain fatty acid (SCFA) concentrations (P > 0.050). However, during BASE and CHAL, SA heifers experienced greater linear (P = 0.031), quadratic (P = 0.016), and cubic (P = 0.008) coefficients for the duration of time that pH was <5.5. In addition, a treatment × day interaction for the duration that pH was <5.5 during REC1 suggested that LA cattle tended to recover from the challenge more rapidly than SA cattle (P = 0.085). Regression analysis confirmed that the LA heifers experienced a quicker linear (P = 0.019) recovery from induced acidosis over time. These results indicate adaptation of the ruminal epithelium continues with advancing time as evidenced by more stable ruminal pH both before and after an induced bout of acute ruminal acidosis but does not affect susceptibility of cattle to ruminal acidosis.

Moderate decreases in the forage-to-concentrate ratio before feed restriction and increases thereafter independently improve the recovery from a feed restriction insult in beef cattle

The objective of this study was to determine if the forage-to-concentrate ratio (F:C) of diets fed prior to and during (PRE) feed restriction (FR) and diets fed post-FR (POST) affect the recovery for DMI, ruminal fermentation, and short-chain fatty acid (SCFA) absorption following FR. Twenty ovariectomized and ruminally cannulated Angus × Hereford heifers were used in this study and were fed (ad libitum) either a high forage (HF; F:C = 92:8) or a moderate forage (MF; F:C = 60:40) diet for 19 d. Heifers were then exposed to a 5-d FR period where feed was restricted to 25% of ad libitum intake relative to that measured during the previous 5 d. After FR, heifers were provided feed ad libitum with one half of the HF and MF heifers receiving the HF or MF diet during the 3-wk recovery period (REC1, REC2, and REC3). This resulted in 4 treatment combinations separated over time (PRE-POST): HF-HF, HF-MF, MF-HF, and MF-MF. The PRE × POST interaction was not significant for any of the measured variables, and the PRE × POST × period interaction was only significant for the molar proportion of ruminal butyrate. For heifers fed HF PRE, DMI increased from REC1 to REC3 whereas DMI did not differ among periods for heifers fed MF PRE (PRE × period, P = 0.045). The duration that pH < 5.5 (PRE × POST; P = 0.003) was numerically greater during REC1 for heifers fed HF than MF PRE (191 vs. 98 min/d), with duration decreasing from REC1 to REC2 for heifers fed HF PRE. Total ruminal SCFA concentration and absorption rate were not affected by the diet fed PRE (P > 0.05) or period (P > 0.05). For heifers fed MF POST, DMI increased from REC1 to REC3 whereas DMI did not differ among POST periods for heifers fed HF POST (POST × period, P = 0.033). The duration that ruminal pH was <5.5 was greater for heifers fed MF than HF POST (274.9 vs. 14.1 min/d; POST × period, P < 0.001) with MF heifers decreasing duration from REC1 to REC2 whereas duration did not differ among periods for HF. Ruminal SCFA concentration and rate of absorption were not affected (P > 0.05) by diet fed POST. It is concluded that feeding a MF diet prior to and during FR improves the recovery response for DMI. Irrespective of the prefeeding, however, a HF diet is beneficial in the POST-restriction period because it most effectively alleviated ruminal pH reduction and hastened DMI recovery.