Effect of insulin, carbohydrate and branch chain amino acids on milk protein

Research Supervisors:
Dr Frank Dunshea (VIAS and Farrer Centre), Dr Morley Muralitharan (CSU), Dr Ian McCauley (VIAS and Farrer Centre), Dr Nick Robinson (VIAS and Farrer Centre), Dr Helen McPhartlen (VIAS and Farrer Centre) and Dr Simon Sturt (CSIRO)

Funding:
$109,000 PRDC

Duration:
1997-1998

Summary:
The aims of the research were:

1. To determine whether dietary supplementation with branch chain amino acids and infusion of exogenous insulin and dextrose in the lactating sow will increase milk protein secretion.

2. To determine whether determine whether dietary supplementation with branch chain amino acids and daily injection of long acting insulin in the lactating sow will increase piglet growth under commercial conditions.

Rationale for the research:
Sow milk composition is a serious constraint to pre-weaning growth. The pig has evolved to have a high fat milk which ensures survival of piglets born into relatively harsh environments with very little insulation or energy reserves (Mellor and Cockburn, 1986). However, today pigs are kept in more comfortable settings and do not require a milk with such a high fat (relative to protein) content. Attempts to manipulate the milk protein content through simply increasing the protein content of the sow diet have made very little impression on the protein content of milk. It has similarly proved difficult to manipulate milk protein content in the dairy cow through altering dietary protein. However, McGuire et al (1995) recently demonstrated that simultaneous infusion of insulin and glucose into lactating dairy cows increased milk protein percent and yield without changing milk yield. Milk protein yield was dramatically improved if supplemental protein (as abomasal infusions of casein) were provided in addition to the insulin/glucose infusion (Griinari et al. 1997). The aim of this project was to determine whether sow milk protein can similarly be manipulated by infusion/feeding of insulin, glucose and high quality protein.
The project involved two experiments. The first experiment involved simultaneous infusion of insulin and dextrose in to sows that were fed a conventional lactation diet or a diet fortified with protein and the branch chain amino acids valine, isoleucine and leucine. The second study was conducted under commercial conditions and involved daily injection of insulin to sows that were fed a conventional lactation diet or a diet fortified with protein and the branch chain amino acids valine, isoleucine and leucine.

Conclusions:
The first study demonstrated that increasing the dietary protein/BCAA content of the sow diet can increase milk protein content (+10%) but not milk yield. Also, combined infusion of insulin and dextrose increased milk (10%), milk lactose (16%) and milk protein (7%) yields but not milk protein content. These effects were additive and resulted in increased piglet growth (+20%). In the second study it appeared that with the dose and/or mode of administration employed that daily injection of long-acting insulin had no effect upon lactational performance, at least under the commercial conditions under which this study was conducted. Also, increasing the dietary protein level and fortifying the diet with BCAA had no effect on lactational performance. It is likely that the exceptional growth rates exhibited by the sucking pigs in the secondf study (ca. 280 g/d) meant that either the sows and/or the piglets were already performing close to potential. However, these data should not negate those generated in Experiment 1 where quite clear benefits of insulin and glucose infusions coupled with increased dietary protein and BCAA were seen on increased milk protein yield and piglet performance. Further studies should be conducted to separate the dextrose and insulin effects and determine whether there are more appropriate means of manipulating the insulin/glucose/BCAA axis to increase milk protein yield and piglet growth. Also, it is important that these mechanisms be further explored in first litter sows which generally have poorer performance