The nutritive value of separated milk for pigs. I. A comparison of two diets containing separated milk with a standard all-meal diet

The nutritive value of separated milk for pigs: II. The effects of different amounts on performance to 90 kg live weight

Each of seven diets containing different proportions of separated milk and barley meal, supplemented with minerals and vitamins, was given to five groups of four pigs. The ratios of barley to milk solids were such that the crude protein of the dry matter given to pigs of 20 to 40 kg live weight ranged from approximately 15 to 21%. Within each treatment, the proportion of milk was gradually adjusted so that the crude protein level was reduced by 3% over the live-weight range 40 to 91 kg. Daily energy allowances of all pigs were governed by the same scale.

The total dry matter consumed by the pigs had mean total lysine levels of from 0·52 to 1·18% (approximately 0·1% lysine between successive treatments).

Pigs on the lowest level of milk grew more slowly and had poorer feed conversion than other animals.

Percentage dissectable lean in the trimmed side was highly correlated with lysine level. Within the range studied, each 0·1% increase in lysine increased lean by 0·69% and caused decreases in fat thickness. The performance of the milk-fed pigs was compared to controls given a standard all-meal diet.

Nitrogen metabolism trials were carried out on the milk diets. Beneficial responses in terms of nitrogen retention were found up to the highest level of milk given to pigs between 16 and 90 kg live weight.

Genetic relationships of reproduction with growth and with carcass traits in British pigs

Data werfe analysed of litters from Large White and Landrace herds which were tested at central stations in Great Britain for growth and carcass traits. Information on reproductive performance of young females was combined with data on their relatives at central stations in order to calculate genetic relationships of reproduction with growth and with carcass traits. Progeny testing of boars for both sets of traits was the most efficient of the methods considered for this analysis.

In general, the estimated genetic correlations of reproductive performance with growth and with carcass traits were alike in sign for the two breeds, and the signs of the matrix of values were internally consistent. For example, combining data for litter sizes in the Large White breed, genetic correlations were −0·15 (food conversion ratio), 0·06 (daily gain), −0·18 (average backfat depth), −0·63 (killing-out percentage) and −0·41 (hind quarter percentage). When the growth and carcass traits were combined as total points score in a selection index, the genetic correlation between this score and reproductive performance was very small, with a range from −0·04 to 0·02. Calculations showed that inclusion of reproductive performance in the index would increase the rate of genetic improvement by only 0·55%.