T.J. DeVries

Repeated Ruminal Acidosis Challenges in Lactating Dairy Cows at High and Low Risk for Developing Acidosis: Feed Sorting

An experiment was conducted to determine whether the susceptibility of cows to ruminal acidosis influences feed sorting and whether feed sorting changes during a bout of ruminal acidosis. Eight ruminally cannulated cows were assigned to 1 of 2 acidosis risk levels: low risk (LR, mid-lactation cows fed a 60% forage diet) or high risk (HR, early lactation cows fed a 45% forage diet). As a result, diets were intentionally confounded with milk production to represent 2 different acidosis risk scenarios. Cows were exposed to an acidosis challenge in each of two 14-d periods. Each period consisted of 3 baseline days, a feed restriction day (restricting TMR to 50% of ad libitum intake), an acidosis challenge day (1-h meal of 4 kg of ground barley/wheat before allocating the TMR), and a recovery phase. Ruminal pH was measured continuously for the first 9 d of each period using an indwelling system. Feed and orts were sampled for 2 baseline days, on the challenge day, and 1 and 3 d after the challenge day for each cow and subjected to particle size analysis. The separator contained 3 screens (18, 9, and 1.18 mm) and a bottom pan to determine the proportion of long, medium, short, and fine particles, respectively. Sorting was calculated as the actual intake of each particle size fraction expressed as a percentage of the predicted intake of that fraction. All cows sorted against the longest and finest TMR particles and sorted for medium-length particles. Sorting was performed to a greater extent by the HR cows, and this sorting was related to low ruminal pH. Both HR and LR cows altered their sorting behavior in response to acidosis challenges. For the HR cows, severe acidosis was associated with increased sorting for the longer particles in the diet and against the shorter particles, likely to lessen the effects of the very.

Repeated ruminal acidosis challenges in lactating dairy cows at high and low risk for developing acidosis: ruminal pH.

The primary objective of this experiment was to determine whether lactating dairy cows that are at high (HR) or low (LR) risk for experiencing ruminal acidosis, because of their diet and stage of lactation, differ in their response to an acidosis challenge. A secondary objective was to determine whether the severity of acidosis changes with repeated challenges. The experiment was a completely randomized design with 2 groups (risk scenarios, HR vs. LR) and 3 periods corresponding to 3 repeated acidosis challenges. Eight lactating ruminally cannulated cows were assigned to 1 of 2 groups: HR, early lactation cows fed a 45% forage diet, or LR, midlactation cows fed a 60% forage diet. Cows were exposed to 3 acidosis challenges, each separated by 14 d. The challenge consisted of restricting total mixed rations to 50% of ad libitum intake for 24 h, followed by a 1-h meal of 4 kg of ground barley-wheat before allocating the total mixed rations. Ruminal pH was measured continuously for 9 of the 14 d each period using an indwelling system. Subacute acidosis (SARA) was described at 2 thresholds: pH <5.8 and pH <5.5. As expected, HR cows had lower ruminal pH profiles (curves) compared with LR cows: mean pH (5.81 vs. 6.21) and nadir pH (5.13 vs. 5.53). The HR cows also experienced SARA to a greater extent than LR cows during the experiment (pH <5.8, 10.6 vs. 3.5 h/d; pH <5.5, 5.9 vs. 1.6 h/d). The pH profiles of cows in both risk categories decreased with each challenge period; mean pH was 6.13, 6.03, 5.77, and nadir pH was 5.52, 5.34, and 5.14 in periods 1, 2, and 3, respectively. The challenges caused a similar decrease in pH for cows in both risk categories, but because the HR cows had a lower baseline pH, they experienced more severe SARA with each subsequent challenge. Feed restriction the day before administering the acidosis challenge caused ruminal pH to gradually increase. On the challenge day, the entire grain allotment was consumed by all cows in period 1, six cows in period 2, and only 3 cows in period 3. The pH plummeted immediately after each grain challenge. Ruminal pH remained very low during the first day after the challenge for all cows, but LR cows began their recovery more quickly than HR cows. Regardless of risk category, with each successive challenge, the pH decrease on the challenge day was more severe: nadir pH on the challenge day was 5.19, 5.07, and 4.90 and duration of SARA (pH <5.8) was 12.2, 13.4, and 15.8 h/d in periods 1, 2, and 3. This study indicates that cows become more prone to acidosis over time even though they decrease intake of the challenge grain to avoid acidosis. The severity of each subsequent bout of acidosis increases, especially for cows fed diets low in physically effective fiber and at high acidosis risk. Therefore, a bout of acidosis that occurs due to improper feed delivery or poor diet formulation can have long-term consequences on cow health and productivity.

The effects of feed bunk competition on the feed sorting behavior of close-up dry cows.

The objectives of this research were to describe the feed sorting, feeding behavior, and feed intake of cows consuming a close-up ration and to determine if these behaviors are affected by competition for access to the feed bunk. Thirty-six dry Holstein cows, consuming a close-up total mixed ration diet, were assigned to 1 of 2 treatments: 1) noncompetitive (1 cow/feed bin) or 2) competitive (2 cows/feed bin). Dry matter intake, feeding behavior, and sorting behavior were monitored for each feed bin on 4 separate days during wk 2 and 3 before the anticipated calving dates of the cows. Fresh feed and orts were sampled daily from each bin and were subjected to particle size analysis. The particle size separator consisted of 3 screens (18, 9, and 1.18 mm) and a bottom pan resulting in 4 fractions (long, medium, short, and fine). Sorting was calculated as the actual intake of each particle size fraction expressed as a percentage of the predicted intake of that fraction. Regardless of treatment, the cows sorted against long particles and for short and fine particles. Competition at the feed bunk had no effect on the sorting behavior, dry matter intake, or feeding time of the cows, but did dramatically increase the feeding rate of the cows. The competitively fed cows also had fewer meals per day, and tended to have larger and longer meals. Our results suggest that increased competition at the feed bunk promotes feeding behavior patterns that will likely increase the between-cow variation in composition of total mixed ration consumed.

Repeated ruminal acidosis challenges in lactating dairy cows at high and low risk for developing acidosis: Feeding, ruminating, and lying behavior

An experiment was conducted to determine whether the susceptibility to ruminal acidosis, as defined through differences in days in milk (DIM), milk production level, and ration composition, influences cow feeding, ruminating, and lying behavior and whether these behaviors change during an acute bout of ruminal acidosis. Eight ruminally cannulated cows were assigned to 1 of 2 acidosis risk levels: low risk (LR, mid-lactation cows fed a 60:40 forage:concentrate ratio diet) or high risk (HR, early lactation cows fed a 45:55 forage:concentrate diet). As a result, diets were intentionally confounded with DIM and milk production to represent 2 different acidosis risk scenarios. Cows were exposed to an acidosis challenge in each of three 14-d periods. Each period consisted of 3 baseline days, a feed restriction day (restricting total mixed ration to 50% of ad libitum intake), an acidosis challenge day (1 h meal of 4 kg of ground barley/wheat before allocating the total mixed ration), and a recovery phase. Feeding, rumination, and standing/lying behavior were recorded for 2 baseline days, on the challenge day, and 1 and 4 d after the challenge day for each cow. Across the study, there were no differences in measures of standing, lying, or feeding behavior between the 2 groups of cows. The HR cows did, on average, spend less time ruminating (491 vs. 555 min/d) than the LR cows, resulting in a lesser percentage of observed cows ruminating across the day (44.6 vs. 48.1%). The acidosis challenge resulted in changes in behavior in all cows. Compared with the baseline, feeding time increased on the first day after the challenge (395 vs. 310 min/d), whereas lying time decreased (565 vs. 634 min/d). Rumination time decreased the first day following the challenge (436 min/d) relative to the baseline (533 min/d), but increased the following day (572 min/d). Fewer cows were observed to be ruminating at a given time on the first day following the challenge as compared with the baseline period. Despite this, on a herd level, numerous observations of the proportion of cows ruminating at any one time would need to be taken to accurately detect an acute bout of acidosis using changes in rumination behavior. Overall, these results suggest that risk of acidosis may have little overall effect on general behavior, with the exception of rumination. Furthermore, an acute bout of acidosis alters behavioral patterns of lactating dairy cows, particularly rumination behavior, and identification of these changes in behavior through repeated measurements may assist in the detection of an acidosis event within a herd.

The effect of meloxicam on pain sensitivity, rumination time, and clinical signs in dairy cows with endotoxin-induced clinical mastitis

The objectives of this study were to (1) evaluate the use of a pressure algometer and an automated rumination monitoring system to assess changes in pain sensitivity and rumination time in response to endotoxin-induced clinical mastitis and (2) evaluate the effect of the nonsteroidal antiinflammatory drug meloxicam on pain sensitivity and rumination time, as well as other clinical signs, in dairy cattle with endotoxin-induced clinical mastitis. Clinical mastitis was induced in 12 primiparous and 12 multiparous lactating dairy cows by intramammary infusion of 25 µg of Escherichia coli lipopolysaccharide (LPS) into 1 uninfected quarter. Immediately after, half the cows were injected subcutaneously with meloxicam (treated group) and half with the same volume of a placebo solution (control group). Pain sensitivity was assessed by measuring the difference in pressure required to elicit a response on the control and challenged quarter using an algometer 3 d before, immediately before, and at 3, 6, 12, and 24h after LPS infusion and either meloxicam or placebo injection. Rumination was continuously monitored from 2 d before to 3 d after LPS infusion using rumination loggers. Udder edema, body temperature, somatic cell score, and dry matter intake were also monitored to evaluate the occurrence and the duration of the inflammation after LPS infusion. In control animals, the difference in the pressure applied to the control and challenged quarters (control - challenged quarter) increased by 1.1 ± 0.4 kg of force 6h after LPS infusion compared with the baseline, suggesting an increase in pain sensitivity in the challenged quarter. Neither the LPS infusion nor the meloxicam treatment had an effect on daily rumination time. However, the rumination diurnal pattern on the day of LPS infusion showed an overall deviation from the baseline pattern. Cows spent less time ruminating in the hours following LPS infusion and more time ruminating later in the day. Meloxicam did not alter somatic cell score or dry matter intake. However, meloxicam-treated animals had less udder edema and a lower body temperature in the hours following LPS infusion compared with control animals. In conclusion, pressure algometers and rumination loggers show promise as tools to detect mastitis and monitor recovery on farm. Further, meloxicam has a beneficial effect in relieving pain and decreasing udder edema and body temperature in LPS-induced clinical mastitis.

Short communication: Feeding method affects the feeding behavior of growing dairy heifers

There is limited information available on what is the most appropriate feeding method for growing dairy heifers. The objective of this study was to determine the effect of feeding method on the feeding behavior and diet selection of growing dairy heifers. Six prepubescent Holstein heifers (158.2 +/- 4.0 d old, weighing 168.2 +/- 15.7 kg), fed once per day for 1.0 kg/d of growth, were subjected to each of 3 treatments in 3 successive 7-d treatment periods using a replicated 3 x 3 Latin square design. Treatments consisted of feeding 2.02 kg/d dry matter of grain concentrate and ad libitum chopped grass hay as: 1) choice (grain concentrate and hay in separate feed bins), 2) top-dressed ration (grain concentrate placed on top of the hay in one feed bin), and 3) total mixed ration (TMR, grain concentrate mixed with hay in one feed bin). Dry matter intake (DMI) and feeding behavior were monitored for 7 d for each animal on each treatment, and feed sorting was monitored for the last 3 d of each treatment period. The provision of grain concentrate and hay in either a choice or top-dressed situation resulted in young dairy heifers rapidly consuming the grain concentrate portion of their ration in very few, large meals before consuming the hay portion of their ration. The provision of the 2 ration ingredients as a TMR increased the distribution of DMI over the day and reduced the amount of sorting (against long forage particles, and for short grain concentrate particles) by heifers. These results suggest that the provision of a TMR to growing dairy heifers, as opposed to feeding concentrate and hay as either a choice or top-dressed, promotes a more balanced intake of nutrients across the day.

Nutrient intake and feeding behavior of growing dairy heifers: effects of dietary dilution.

The objective of this study was to determine how the addition of straw to a total mixed ration offered to growing dairy heifers affects their nutrient intake and feeding behavior. Six prepubescent Holstein heifers (226.2 +/- 6.3 d old and weighing 250.1 +/- 17.7 kg), fed once per day for 1.0 kg/d of growth, were subjected to each of 3 treatment diets using a replicated 3 x 3 Latin square design. The treatment diets were 1) control (17.0% corn silage, 52.1% grass silage, 30.9% concentrate), 2) control diet with 10% straw, and 3) control diet with 20% straw. Dry matter intake and feeding behavior were monitored for 7 d for each animal on each treatment. Fresh feed and orts were sampled on the last 3 d of each treatment period for each heifer and were then subjected to particle size analysis. The particle size separator contained 3 screens (19, 8, and 1.18 mm) and a bottom pan, resulting in 4 fractions (long, medium, short, and fine). Sorting activity for each fraction was calculated as actual intake expressed as a percentage of the predicted intake. Heifers sorted against long particles and for short particles on all 3 diets. On the 10 or 20% straw diets the heifers sorted for medium particles. Heifers also sorted for fine particles on the 20% straw diet. There was a linear increase in sorting for medium, short, and fine particles with increased straw in the diet. Dry matter intake linearly decreased with increased straw in the diet. Feeding time and meal duration increased linearly with the addition of straw to the diet, whereas feeding rate, meal size, and meal frequency decreased with the addition of straw. Requirements for maintenance and growth of 1.0 kg/d were sufficiently met when the animals consumed the control and 10% straw diet. On the 20% straw diet the animals consumed sufficient nutrients to achieve a 0.9 kg/d growth rate. These results indicate that the addition of straw to the diet of prepubescent heifers strongly influences their sorting behavior. Despite this sorting, the results suggest that a low-quality feedstuff may be included in the diet to target nutrient intake and reduce feed costs without negatively affecting feeding behavior or growth potential.

Manageable risk factors associated with the lactational incidence, elimination, and prevalence of Staphylococcus aureus intramammary infections in dairy cows

Staphylococcus aureus intramammary infections (IMI) are a major cause of mastitis on farms worldwide. Incidence and elimination rates are the key determinants of prevalence of Staph. aureus, and risk factors associated with these rates must be identified, prioritized, and controlled to obtain long-term reduction in prevalence. The objectives of this study were to identify manageable risk factors associated with the lactational incidence, elimination, and prevalence of Staph. aureus IMI. A cohort of 90 Canadian dairy farms was recruited and followed in 2007 and 2008. Quarter milk samples were collected repeatedly from a selection of cows, and bacteriological culture was realized to assess incidence, elimination, and prevalence of Staph. aureus IMI. Practices used on farms were measured using direct observations and a validated questionnaire. A linear regression model was used to explore the relationship between herd IMI prevalence and incidence and elimination rates. Multilevel logistic regression models were used to compute measures of associations between practices used on farms and IMI incidence, elimination, and prevalence. The herd incidence rate was the most important predictor of herd IMI prevalence: a reduction of the incidence rate equivalent to its interquartile range (0.011 new IMI/quarter-month) was associated with a prevalence reduction of 2.2 percentage points; in comparison, an equivalent increase of the elimination rate by its interquartile range (0.36 eliminated IMI/quarter-month) resulted in a prevalence reduction of 0.4 percentage points. Postmilking teat disinfection and blanket dry-cow therapy were already implemented by most herds. Most of the practices associated with Staph. aureus IMI incidence were related to milking procedures. Among these, wearing gloves during milking showed desirable associations with IMI incidence, elimination, and prevalence. Similarly, adequate teat-end condition and use of premilking teat disinfection were associated with lower IMI incidence and prevalence. The initial herd prevalence of Staph. aureus IMI was positively associated with subsequent IMI incidence. This indicates that, in some situations, an initial reduction of the pool of infected quarters could be justified. Some housing practices were associated with IMI incidence, elimination, or prevalence. The effects of these latter practices, however, were often influenced by specific cow characteristics such as parity or days in milk. These results highlight the importance of good milking practices to prevent Staph. aureus IMI acquisition and, therefore, reduce their prevalence.

Effect of physical form of forage on performance, feeding behavior, and digestibility of Holstein calves

The physical form of forage may influence rumen development and, consequently, the body weight gain, dry matter (DM) consumption, digestibility, and welfare of dairy calves. The objective of this study was to determine the effect of 2 different physical forms of forage on performance, apparent digestibility, and feeding behavior of young calves. Twenty Holstein male calves (46.8 ± 1.2 kg) were randomly assigned at birth to 1 of 2 feeding treatments in which they were exposed to a mixed ration containing (on a DM basis) 90% crumb starter concentrate and either (1) 10% coarsely chopped (3 to 4 cm) grass hay (CRS; n=10) or (2) 10% finely ground (2mm) grass hay (FN; n=10). All calves were offered 8L/d of milk replacer (MR; 1.2 kg of DM) from birth; the amount of MR was progressively reduced after 5 wk to enable weaning by the end of wk 7. The study finished after wk 8. Consumption of the mixed ration, MR, and water was recorded daily, and calves were weighed twice weekly. Samples of feed and orts were taken in wk 7 and 8 for nutrient content analysis. Behavioral data for each calf were obtained for 2h/d during wk 6 and 8, for a total observation time per animal of 28 h. Total feces were collected during wk 8 to determine apparent digestibility. Calves fed CRS had greater DM intake than those fed FN (2.70 vs. 2.45 ± 0.11 kg/d, respectively) during the week after weaning (wk 8). Body weight gain was similar between treatments; however, calves fed CRS tended to have a greater gain-to-feed ratio than calves fed FN (0.68 vs. 0.63 ± 0.02 kg of gain/kg of DM intake). No differences were observed in crude protein and acid detergent fiber consumption between treatments; however, calves fed CRS tended to consume more neutral detergent fiber than calves fed FN during the last week of the study (719.2 vs. 610.5 ± 25.84 g/d). Calves receiving CRS sorted in favor of neutral detergent fiber to a greater extent than calves consuming FN, whereas calves fed FN sorted in favor of crude protein to a greater extent than calves fed CRS. Apparent DM, crude protein, neutral detergent fiber, and acid detergent fiber digestibility values were greater in calves fed CRS than in those fed FN (72.3, 77.4, 40.7, and 42.7% vs. 69.2, 74.5, 34.0, and 35.6%, respectively). Calves fed FN spent more time performing nonnutritive oral behaviors than those fed CRS, and calves fed FN tended to spend less time idle (either lying or standing) than those fed CRS. In conclusion, providing chopped hay to young calves improved feed intake, DM, crude protein, neutral detergent fiber, and acid detergent fiber digestibility values during the week after weaning, and reduced nonnutritive oral behaviors compared with offering ground hay.

Associations of housing, management, milking activity, and standing and lying behavior of dairy cows milked in automatic systems

The objective of this cross-sectional study was to describe the housing, feeding management, and characteristics (parity and stage of lactation) of cows on commercial automatic milking system (AMS) dairies and their associations with the standing and lying behavior patterns and milking activity (frequency and yield) of lactating dairy cows. Thirteen AMS herds were enrolled in the study, with an average herd size of 71±30 (mean ± SD; range: 34 to 131) lactating cows. All of the herds used freestall barns, each set up for free cow traffic to the AMS. On-farm measurements were taken to determine stocking density at the freestalls (0.9±0.1 cows/stall; mean ± SD), feed bunk (0.66±0.17 m of feed bunk space/cow; mean ± SD), and AMS units (55±11 cows/AMS; mean ± SD). A random sample of 30 cows/herd was selected to monitor standing and lying behavior for 4d using electronic data loggers. Times of feed delivery and feed push-up were recorded daily by the herd managers. Milking times, frequency, and yield were automatically recorded by the AMS units. Data were analyzed in a multivariable mixed regression model to determine which herd-level (housing and feeding management) and cow-level (parity, DIM, and milk yield) factors were associated with behavior and milking activity measures. Lying bout lengths were found to be negatively associated with milk yield and tended to be positively associated with more space at the feed bunk. Increased lying duration was associated with cows of lower milk production, increased space at the feed bunk, and increased frequency of feed push-up. Longer postmilking standing durations were associated with cows of higher parity. An association existed between cows milking less frequently when they were further in lactation, were of higher parity, and as stocking density at the AMS (cows/AMS) increased. Milk yield was positively associated with increased space at the feed bunk and higher parity and negatively associated with DIM. From this study, it can be concluded that increased milking frequency may be achieved in AMS herds by reducing stocking density at the AMS unit. Further, in AMS systems, greater milk yield and lying duration may be achieved by ensuring that cows have ample feed bunk space and have their feed readily available to them in the bunk.