Low milk protein concentrations: nutritional causes and cures

Date: 18 May 2004 Author: Brad Granzin

Introduction

Prior to deregulation, payment schemes often encouraged lower concentrations of components in milk. Under a deregulated marketplace, a greater payment emphasis has been placed on milk fat and milk protein concentrations. This article outlines the major nutritional factors that affect milk protein concentrations, and offers some suggestions on how to improve them.

In NSW, November through to March is often a period of low milk protein concentrations for many producers. A farm survey sponsored by the Dairy Research and Development Corporation (DRDC) has been undertaken in south-east Queensland; its purpose was to identify the major factors causing low milk protein concentrations. The results show that genetics, nutrition, stage of lactation and weather conditions affect milk protein concentrations either independently or by interacting with each other. This probably explains why many nutritional approaches have not improved milk protein concentrations. It is generally recognised that it is difficult to nutritionally change milk protein concentrations by more than 0.2%.

Energy balance

Energy intake (as opposed to protein intake) is often the major driver of milk protein synthesis. Cows which are in a large negative energy balance (e.g. pasture-fed high-genotype cows supplemented with low levels of grain) have low milk protein concentrations, e.g. 2.8–2.9%. Increasing grain feeding levels in these circumstances can (but does not always) increase milk protein concentrations; however, this improvement will probably be detrimental to pasture utilisation unless stocking rates are increased.

Grain type

A DRDC-funded experiment at Wollongbar during 2001 has shown that early-lactation cows fed maize-based supplements while grazing kikuyu have higher milk protein concentrations than cows fed barley-based supplements (see Table 1). We expect this is because the energy from maize is digested more efficiently than the energy from barley.

Feeding rate: 5 kg/cow/day as fed

When cows were fed at 5 kg/cow/day, economic calculations based on the results of this study and on the various payment systems for manufacturing milk ($2.50/kg fat + $4.50/kg protein; $3.00/kg fat + $3.00/kg protein) show that there was little difference in returns (+1 to 4.2c per cow per day) between grains.

Feeding rate: 9 kg/cow/day as fed

When the feeding rate was 9 kg/cow/day, maize had an economic advantage (+23 to 25c per cow per day) under either pay system. Based on this, you could afford to pay an extra $26 to $28 per tonne for maize and still come out in front. Unfortunately, maize is often very expensive during summer months in NSW. It remains unclear whether or not grains which are digested at similar slow rates (e.g. hammermilled sorghum, steam-flaked barley) offer similar benefits to milk protein concentrations during summer.

Effects of level of supplementation and grain type on milk production and liveweight change of cows grazing kikuyu at Wollongbar (January to March 2001)
ParameterBarleyCorn
Level of feeding
(kg/cow/day as fed)
5959
Milk yield (L/day) 20.1 23.2 20.1 23.9
Fat (%) 3.49 3.30 3.66 3.20
Protein (%) 2.702.722.902.92
Lactose (%) 4.95 4.95 4.92 4.99
Yields (g/day):     
Fat 687 751 719 732
Protein 529 627 572 665
Change in liveweight (kg/day) 0.45 0.49 0.39 0.13

Protein intake

Cows fed high levels of grain in combination with poor quality tropical grasses would respond, in terms of milk yield and milk protein concentration, to supplementary protein. This situation is fairly rare, as well-managed tropical grass swards usually have high protein concentrations.

Effects of heat

A result from the south-east Queensland survey has shown that hot, humid conditions have a negative effect on milk protein concentrations. This effect is probably due to the reduction in feed intake (and hence energy intake) caused by these weather conditions. Work carried out at Mutdapilly in Queensland has shown that there is a 0.1% increase in milk protein concentration when cows are cooled by using shade and sprinklers during periods of heat stress.

DISCLAIMER

NSW DPI is not liable for any losses in production or damage arising from the recommendations in this article due to the variation in the nutrient content of feedstuffs and inaccurate formulations.