P. T. Doyle

Profitable feeding of dairy cows on irrigated dairy farms in northern Victoria

Milk production per cow and per farm in the irrigated region in northern Victoria have increased dramatically over the past 2 decades. However, these increases have involved large increases in inputs, and average productivity gains on farms have been modest. Before the early 1980s, cows were fed predominantly pasture and conserved fodder. There is now large diversity in feeding systems and feed costs comprise 40–65% of total costs on irrigated dairy farms. This diversity in feeding systems has increased the need to understand the nutrient requirements of dairy cows and the unique aspects of nutrient intake and digestion in cows at grazing. Principles of nutrient intake and supply to the grazing dairy cow from the past 15 years’ research in northern Victoria are summarised and gaps in knowledge for making future productivity gains are identified. Moreover, since the majority of the milk produced in south-eastern Australia is used in the manufacture of products for export, dairy companies have increased their interest in value-added dairy products that better meet nutritional requirements or provide health benefits for humans. Finally, some examples of the impacts of farm system changes on operating profit for some case study farms in northern Victoria are presented to illustrate the need for thorough analysis of such management decisions.

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.

Calculating dry matter consumption of dairy herds in Australia: the need to fully account for energy requirements and issues with estimating energy supply

Feed costs are the major component of the variable costs and a significant component of the total costs of milk production on Australian dairy farms. To improve farm productivity, farmers need to understand how much feed is being consumed and the nutritive characteristics of the diet. This paper reviews an existing simple approach, the ‘Target 10’ approach, which is commonly used by the dairy industry in Victoria to estimate annual forage consumption. An alternative approach – the ‘Feeding Systems’ approach – is then introduced. The ‘Feeding Systems’ approach is compared with estimated forage consumption measured under experimental conditions. An analysis of the sensitivity of both approaches to incremental changes in key variables is presented. The ‘Feeding Standards’ approach was concordant with estimated forage consumption measured under experimental conditions. Sensitivity analysis has highlighted key variables which may have considerable influence over simulated forage consumption using this approach. Given that none of the key variables tested in this analysis can be varied in the ‘Target 10’ approach, we feel confident that the ‘Feeding Standards’ approach provides an improved method of back-calculating annual on-farm forage consumption. Using a robust approach to calculate forage consumption which fully accounts for metabolisable energy requirements is important where farmers are using home-grown forage consumption as an indicator of farm feeding system performance. It is also important to understand the assumptions involved in estimating metabolisable energy supply from either supplements or forage.

Evaluating options for irrigated dairy farm systems in northern Victoria when irrigation water availability decreases and price increases

A case study and spreadsheet modelling approach was used to examine options for two dairy farms in northern Victoria that would enable them to maintain profit, or ameliorate a decline in profit, under changes in irrigation water availability and price. Farm 1 obtained 43% of estimated metabolisable energy requirements for the milking herd from supplements, had a predominantly spring-calving herd, and used mainly owner/operator labour. Farm 2 obtained 54% of estimated metabolisable energy requirements for the milking herd from supplementary feeds, had a split-calving herd, and used owner/operator and employed labour. When long-term allocation of irrigation water declined from 160% to 100% water right (WR), the ‘base farm’ system for both farms was maintained by purchasing temporary water. At a water price of

Increasing the intake of highly digestible Persian clover herbage reduces rumen fluid pH and the rate of degradation of neutral detergent fibre in grazing dairy cows

35/ML and allocation of 160% WR, the operating profit of Farms 1 and 2 was AU

Potential impacts of negative associative effects between concentrate supplements, pasture and conserved forage for milk production and dairy farm profit

52 000 and

Effects of grain or hay supplementation on the chewing behaviour and stability of rumen fermentation of dairy cows grazing perennial ryegrass-based pasture in spring

315 000, respectively. This declined to

Increased profitability and social outcomes from livestock in smallholder crop–livestock systems in developing countries: the ACIAR experience

30 000 and

Predicting milk responses to cereal-based supplements in grazing dairy cows

253 000 at a water availability of 100% WR. In response to changes in water availability and/or price, Farm 1 could purchase more supplements (a mix of grain and fodder) or replace some irrigated perennial pasture with irrigated annual pasture. Purchasing more supplements was not as profitable as buying irrigation water on the temporary market in the long term. At an irrigation water allocation of 130% WR, a water price of

Evaluating the economics of concentrate feeding decisions in grazing dairy cows

35/ML and assumed response to extra supplement of 1.4 L milk/kg, operating profit was