The effect of concentrate supplement type on milk production, nutrient intake, and total-tract nutrient digestion in mid-lactation, spring-calving dairy cows grazing perennial ryegrass (Lolium perenne L.) pasture

The objective of this study was to evaluate the effect of concentrate supplement type on milk production, nutrient intake, and total-tract nutrient digestion in lactating dairy cows grazing mid-season perennial ryegrass (Lolium perenne L.; PRG) pasture. Twelve primiparous (mean ± standard deviation; 95 ± 30 d in milk and 470 ± 43 kg of body weight) and 68 multiparous (99 ± 24 d in milk and 527 ± 64 kg of body weight) lactating dairy cows were blocked based on pre-study milk yield and parity and randomly assigned to 1 of 4 dietary treatments. The 4 dietary treatments were a non-supplemented PRG control (PRG); PRG supplemented with 4.4 kg of dry matter (DM) per cow per day of citrus pulp and 0.067 kg of DM/cow per day of urea (PRG+C); PRG supplemented with 0.8 kg of DM/cow per day of heat-treated soybean meal (PRG+PP); and PRG supplemented with 3.1 kg of DM/cow per day of a combination of heat-treated soybean meal and citrus pulp (PRG+C+PP). The study consisted of a 2-wk adaptation period and a 10-wk period of data collection. Weekly measurements of milk yield, body weight, body condition score, and feeding and rumination time were made. Nutrient intake and total-tract digestibility were measured during wk 6 of the study. A large soil moisture deficit was experienced during the study that probably reduced herbage growth rate and likely altered the chemical composition of the PRG offered when compared with typical mid-season PRG. Total dry matter intake was increased in cows fed PRG+C compared with cows fed PRG and PRG+PP and was similar to cows fed PRG+C+PP (18.0, 15.9, 16.4, and 17.2 ± 0.41 kg of DM/d, respectively). The apparent total-tract neutral detergent fiber digestibility of cows fed the PRG+C diet was lower compared with the PRG and PRG+PP diets and was similar to the PRG+C+PP diet (0.67, 0.70, 0.70, and 0.69 ± 0.01 g/g, respectively). The energy-corrected milk (ECM) yield of cows fed PRG+C+PP was highest (23.7 kg/d), PRG+C was intermediate (22.2 kg/d), and PRG was lowest (20.8 kg/d). Cows fed PRG+PP produced more ECM (22.9 kg/d) compared with cows fed PRG and produced similar ECM compared with cows fed PRG+C and PRG+C+PP diets. The PRG+PP diet increased milk protein yield compared with the PRG diet, tended to increase milk protein yield compared with the PRG+C diet, and was similar to the PRG+C+PP diet. Milk fat concentration and the composition of milk fat were not influenced by treatment. The results demonstrated that, for cows consuming pasture-based diets, increasing metabolizable protein supply allowed higher milk yield as metabolizable protein was more limiting than metabolizable energy. However, due to the large soil moisture deficit experienced during this experiment, caution is recommended when extrapolating these results to cows consuming typical mid-season PRG herbage.

Economic Analysis of Offering Different Herbage Allowances to Dairy Cows Fed a Partial Mixed Ration

Simple Summary

In south-eastern Australia, most dairy cows consume grazed pasture, cereal grain fed in the dairy and hay in the paddock. Previous research has shown that feeding supplements to grazing cows as a well-formulated mixed ration can increase feed intake, milk production and profit. This previous work was conducted under a limited herbage allowance to represent the conditions of drought or a high stocking rate. Two subsequent animal experiments were performed, one in early lactation and the other in late lactation, where the herbage allowance was varied from low to high and used to investigate the economics of partial mixed ration (PMR) feeding. We found that offering a medium allowance (25 and 20 kg DM/cow per day in early and late lactation, respectively) resulted in higher profit (total milk income minus feed costs) than a low herbage allowance (15 and 12 kg DM/cow per day in early and late lactation). No additional profit was obtained by further increasing the herbage allowance from medium to high (40 and 32 kg DM/cow per day in early and late lactation). These findings will assist farmers to manage their PMR systems in a profitable way.

Abstract

The economics of grazing dairy cows offered a range of herbage allowances and fed supplements as a partial mixed ration (PMR) were examined where profit was defined as the margin between total milk income and the cost of pasture plus PMR supplement. The analysis made use of milk production and feed intake data from two dairy cow nutrition experiments, one in early lactation and the other in late lactation. In early lactation and at a PMR intake of 6 kg DM/cow per day, the profit from the cows with access to a medium herbage allowance (25 kg DM/cow per day) was AUD 1.40/cow per day higher than that for cows on a low allowance (15 kg DM/cow per day). At a higher PMR intake of 14 kg DM/cow per day, the profit from the cows on a medium herbage allowance was AUD 0.45/cow per day higher than the cows on a low allowance; there was no additional profit from increasing the herbage allowance from medium to high (40 kg DM/cow per day). In late lactation, the profit from the cows fed a PMR with a medium herbage allowance (20 kg DM/cow per day) was only higher than the cows on a low allowance (12 kg DM/cow per day) when the PMR intake was between 6 and 12 kg DM/cow per day. There was also a difference of AUD +0.50/cow per day between the PMR with medium and high herbage allowance (32 kg DM/cow per day). It was concluded that farmers who feed a PMR to dairy cows should offer at least a medium herbage allowance to optimize profit. While feeding additional PMR increases milk production and profit, further gains would be available by offering a higher herbage allowance. These findings provide an estimate of the net benefits of different herbage allowances when feeding a PMR and will enable farmers to manage their feeding systems more profitably.

Using estimated nutrient intake from pasture to formulate supplementary concentrate mixes for grazing dairy cows

In pasture-based dairy systems, feeding a complex concentrate mix in the parlor during milking that contains cereal grains and protein supplements has been shown to have milk production advantages over feeding straight cereal grain. This experiment had the aim of testing whether further milk production advantages could be elicited by adjusting the composition of the concentrate mix in an attempt to match the expected nutrient intake from pasture during late spring. The experiment used 96 lactating dairy cows, grazing perennial ryegrass pasture offered at a target allowance of 30 kg of dry matter/cow per day (to ground level) during late spring (mid October to November) in southeastern Australia. Cows were allocated into 3 replicates of 4 treatment groups, with 24 cows in each treatment. Each treatment group was offered 1 of 4 dietary treatments in the parlor at milking: control consisting of crushed wheat and barley grains; formulated grain mix (FGM) consisting of crushed wheat, barley, and corn grains and canola meal; designer grain mix 1 (DGM1) consisting of the same ingredients as the FGM grain mix but formulated using the CPM Dairy nutrition model to take into account the expected nutrient intake from pasture; and designer grain mix 2 (DGM2) consisting of the same ingredients as DGM1 but with canola meal replaced by urea and a fat supplement (Megalac, Volac Wilmar, Gresik, Indonesia). Concentrate mixes were offered at 8.0 kg of dry matter/cow per day, except for DGM2 cows, which were offered 7.5 kg of dry matter/cow per day. The experiment ran for a total of 28 d; after a 14-d adaptation period, nutrient intake, milk production, and body weight were measured over a 14-d measurement period. Milk yield (kg) of cows fed the FGM diet was greater than that of the control cows but was not different from that of the DGM1 and DGM2 cows. However, milk fat and protein yields (kg) were greater for cows fed the FGM diet than for all other diets. There was no difference in estimated daily pasture or total dry matter intakes between the 4 treatment groups, despite cows fed the DGM2 treatment consuming less of the concentrate mix (average 6.5 kg of dry matter/cow per day when offered 7.5 kg of dry matter/cow per day). This research has demonstrated the potential for using a nutrition model to take into account the expected nutrient intake from pasture to formulate a concentrate mix (DGM1) to achieve similar milk yields, but also highlighted the need for near real-time analyses of the pasture to be grazed so as to also capture benefits in terms of milk fat and protein yield.

Defining the key attributes of resilience in mixed ration dairy systems

Dairy feeding systems in Australia and New Zealand have seen an increase in the use of mixed rations to manage variability in climate and market conditions and enable a certain degree of resilience in the operating environment. In this review, resilience was defined as the ability of the farm system to respond to challenges, optimise productivity and profitability for a given set of circumstances, and persist over time. Specific attributes of a dairy system that contribute to resilience were considered as flexibility, consistency, adaptation, sustainability and profitability. A flexible forage base that uses water efficient forage species provides a consistent supply of nutrients from home-grown forages across the year and is a key driver of resilience. Consistent milk production from purchased concentrates adds value to the forage base and will ensure that the system is profitable in the long term. Appropriate investment in infrastructure and careful management of debt has a positive impact on technical and financial efficiency and improves overall economic performance and resilience of the system. Nutrients, feed wastage, cow comfort and welfare were also identified as key areas to focus on for improved sustainability. Future research investigating the interaction between forages and concentrates, and the subsequent milk production response will be important for the future resilience of mixed ration systems. Adaptive management at a tactical and strategic level across several technical areas will further underpin the resilience of a mixed ration dairy system, and minimise the impact of climate and price variability. This will have flow on benefits to animal welfare and resource sustainability, which will have a positive impact of the public perception of these systems within the Australian and New Zealand dairy industries.