Rumen function and grazing behavior of early-lactation dairy cows supplemented with fodder beet

Fodder beet (FB) is a source of readily fermentable carbohydrate that can mitigate early spring herbage deficits and correct the negative energy balance experienced during early lactation in pastoral dairy systems of New Zealand. However, the low-fiber and high-soluble carbohydrate content of both FB bulb and spring herbage are factors that promote subacute ruminal acidosis, impairing rumen function and limiting the marginal milk production response to supplement. In a crossover experiment, 8 Holstein Friesian × Jersey early-lactation dairy cows were used to test the effect of supplementing 16 kg of dry matter (DM) of a grazed perennial ryegrass herbage with 6 kg of DM/d of FB bulb (FBH) versus herbage only (HO) on changes in rumen function and grazing behavior. Following 20 d of adaptation to diets, DM disappearance (%) of FB bulb (FBH cows only) and herbage were measured in sacco, separately. Cows were fasted overnight, and the ruminal contents were bailed the following morning (~0930 h) again to determine the pool size of volatile fatty acids, ammonia, and particle size of digesta, as well as to estimate the rate of ruminal outflow and degradation of neutral detergent fiber. The FBH diet did not alter DM intake, milk yield, or milk solid (fat + protein) production compared with HO. Supplementation of herbage with FB reduced ruminal pH compared with HO between ~0800 h and 1300 h each day. During each period, 1 cow experienced severe subacute ruminal acidosis (pH <5.6 for >180 min/d) during final adaptation to the target FB allocation. The FBH diet reduced the ruminal pool of acetate and ammonia, but increased the ruminal pool of butyrate and lactate compared with HO. When fed FB, rumination and grazing time increased and grazing intensity declined compared with cows fed HO. Despite increased rumination, the comminution of large particles declined 28% between the first and second rumen bailing when cows were fed FB, and in sacco DM disappearance of perennial ryegrass declined 18% compared with cows fed HO. These results indicate that grazing dairy cows supplemented with FB (40% of daily intake) increase rumination and mastication intensity to counteract reduced ruminal degradation of ryegrass herbage due to low ruminal fluid pH.

Invited review: An evaluation of the likely effects of individualized feeding of concentrate supplements to pasture-based dairy cows

In pasture-based dairy systems, supplementary feeds are used to increase dry matter intake and milk production. Historically, supplementation involved the provision of the same amount of feed (usually a grain-based concentrate feed) to each cow in the herd during milking (i.e., flat-rate feeding). The increasing availability of computerized feeding and milk monitoring technology in milking parlors, however, has led to increased interest in the potential benefits of feeding individual cows (i.e., individualized or differential feeding) different amounts and types of supplements according to one or more parameters (e.g., breeding value for milk yield, current milk yield, days in milk, body condition score, reproduction status, parity). In this review, we consider the likely benefits of individualized supplementary feeding strategies for pasture-based dairy cows fed supplements in the bail during milking. A unique feature of our review compared with earlier publications is the focus on individualized feeding strategies under practical grazing management. Previous reviews focused primarily on research undertaken in situations where cows were offered ad libitum forage, whereas we consider the likely benefits of individualized supplementary feeding strategies under rotational grazing management, wherein pasture is often restricted to all or part of a herd. The review provides compelling evidence that between-cow differences in response to concentrate supplements support the concept of individualized supplementary feeding.

Increasing amounts of crushed wheat fed with Persian clover herbage reduced ruminal pH and dietary fibre digestibility in lactating dairy cows

Sixteen cows in early lactation were individually fed diets consisting of fresh Persian clover (Trifolium resupinatum)-dominant pasture, offered to all cows at 3.7 kg DM/100 kg liveweight (LW); either alone or supplemented with amounts of crushed wheat ranging from ~0.3 to 0.9 kg DM/100 kg LW (four treatments with four cows per treatment). Cows fed Persian clover alone consumed 19 kg DM/day and total DM intake increased (P < 0.001) in a linear manner as the amount of wheat consumed increased, with no significant effects on clover intake. As the proportion of wheat in the diet increased, dietary neutral detergent fibre (NDF) concentrations declined from 28 to 24%, and in vivo NDF (P = 0.055) and acid detergent fibre (ADF; P = 0.015) digestibilities also declined. There were no significant effects of proportion of wheat in the diet on apparent digestibility of DM, organic matter or gross energy. The extent to which negative associative effects on NDF digestion was associated with the clover could not be determined as it was not possible to distinguish between the NDF derived from clover or wheat, but the decline in ADF digestibility suggested that most of the response lay with the clover since the wheat only contained relatively small amounts of ADF. Ruminal fluid pH was below 6.0 for more than 18 h/day in all cows. There was no effect of wheat in the diet on average ruminal fluid pH, but lowest values during the day were negatively related (P < 0.05) to the proportion of wheat in the diet. As the proportion of wheat in the diet increased, ruminal fluid ammonia-N concentration (P < 0.001) and the acetate + butyrate to propionate ratio (P < 0.001) decreased. The proportion of wheat in the diet did not affect nylon bag estimates of NDF degradation rates for grain or forage. Although most data indicated that effects of proportion of wheat in the diet on the utilisation of consumed nutrients were small, the marginal milk response to additional wheat averaged only 0.9 kg energy-corrected milk/kg DM wheat.

Increasing amounts of crushed wheat fed with pasture hay reduced dietary fiber digestibility in lactating dairy cows

Sixteen cows in mid-lactation (milk yield of 23.8 +/- 2.3 kg/d) were individually fed diets consisting of chopped perennial ryegrass hay, offered at 3 kg of dry matter (DM)/100 kg of body weight (BW), fed either alone or supplemented with amounts of crushed wheat ranging from 0.4 to 1.6 kg of DM/100 kg of BW (increasing at nominal intervals of 0.4 kg of DM/100 kg of BW; 5 nominal treatments in total). Three cows were allocated to each treatment except the mid-range wheat treatment, which had 4 cows. Results were analyzed by regression because the intake of the wheat by cows within treatments varied. The hay was used to reflect the characteristics of summer pastures in southeastern Australia. Feed intake and fecal output were measured to determine digestion coefficients, feeds were incubated in nylon bags in the rumen, and rumen variables were monitored. Estimates of metabolizable energy (ME) of the hay from in vivo or in vitro digestibility were also compared. The digestibility of neutral detergent fiber (NDF) was depressed linearly as the amount of crushed wheat consumed increased to 36% of DM intake. The extent to which negative associative effects on NDF digestion were associated with the hay could not be determined, as it was not possible to distinguish between the NDF from hay and that from wheat. However, acid detergent fiber (ADF) digestion also declined, suggesting that most of the response lay with the hay because ADF was negligible in the wheat. Most data indicated that effects of proportion of wheat in the diet on the utilization of consumed nutrients were small. Despite substitution of wheat for hay reducing the forage intake of cows, there was a positive linear effect on marginal milk responses (1.3 kg of energy-corrected milk/kg of DM wheat). Mean rumen fluid pH declined as the proportion of wheat in the diet increased. The lowest pH for any individual cow during a 24-h period was 5.4, and the amount of time that rumen fluid pH was <6.0 ranged from 0 to 14 h depending on the amount of wheat consumed. It was concluded that these perturbations of the rumen environment were probably sufficient to result in negative associative effects. In addition, estimates of the ME content of the hay were higher when calculated from in vitro compared with in vivo digestibility, which has implications when estimating the amount of feed required for production.

Digestion during continuous culture fermentation when replacing perennial ryegrass with barley and steam-flaked corn

The objective of this study was to quantify the optimal inclusion rate of grain required to maximize nutrient digestion of a diet based on highly digestible pasture. It was hypothesized that maximum digestion would occur at a rate of grain inclusion that resulted in a culture pH of 6.0, reflecting the pH below which fiber digestion would be expected to be compromised. Four dual-flow continuous culture fermenters were used to establish the effects on digestion of replacing freeze-dried, highly digestible ryegrass with 0, 15, 30, and 45% of dry matter as 60% barley, 35% steam-flaked corn, and 5% molasses mix. The respective composite diets were fed twice daily to mimic intake patterns observed in dairy cows offered supplements during milking and offered half their daily allowance of pasture after each milking. Digesta samples were collected during the last 3 d of each of four 9-d experimental periods. Average daily culture pH decreased linearly as proportion of cereal grain in the diet increased, with average daily pH ranging from 6.29 to 5.74. Concentrations of neutral detergent fiber and total fatty acids decreased linearly with increasing proportion of cereal grain in the diet. Digestion of organic matter (OM) was maximized at an interpolated value of 24% grain inclusion and culture pH of 6.0, but the difference in the OM digestibility over the range of grain treatments from 0 to 45% was small (3 percentage units) despite pH changes over a range of 6.3 to 5.7. The relatively small change in OM digestibility was explained by reduced fiber and crude protein digestibilities being balanced by an increased digestion of nonstructural carbohydrate. Although different relationships between ruminal pH and digestibility appear to exist when cows are fed pasture alone compared with a total mixed ration, when starch supplements are included in pasture diets, the relationships associated with feeding a total mixed ration may then be more likely to apply.

Feed conversion efficiency as a key determinant of dairy herd performance: a review

This paper focuses on dairy herd performance in the United Kingdom and southern Australia, where feed costs have been estimated to comprise between 40 and 67% of the total costs of production. The efficiency of conversion of grazed pasture, home grown forages and purchased feeds into milk has a major bearing on farm profit. Feed conversion efficiency (FCE), defined as ‘kg milk of standardised composition with respect to protein and fat concentrations produced per kg feed dry matter consumed’, is a useful measure of the performance of a farm feeding system, but is seldom used by dairy farmers. It could also be defined as ‘g protein plus fat produced per kg feed dry matter consumed’, given that farmers are often paid for these components. The value of estimating FCE on an annual or shorter-term basis is discussed in relation to accepted principles of feed utilisation and dairy cow energy requirements. The implications of feed intake, conversion of ingested nutrients into absorbed nutrients and the subsequent utilisation of these nutrients for milk production or other purposes, as well as the effects of stage of lactation on FCE, are reviewed. Measuring FCE and identifying opportunities for improvement is relatively straightforward in housed feeding systems, but is more problematic under grazing. Hence, approaches and the key assumptions in estimating FCE in grazing situations, as well as possible limitations of these estimates, are discussed. Finally, a case study examining the potential impact of improved nutritional strategies on FCE and on margin over feed costs is presented. It is concluded that, to remain profitable, dairy farmers need to have a sound knowledge of cow nutrition, along with appropriate measures of FCE to monitor the performance of their milk production system. Such indicators of the biological performance of the farming system are most useful when used in conjunction with appropriate measures of economic performance.