New Strategies Improving Feed Efficiency

Feed efficiency is essential in pork production optimizing growth and maximizing nutrient use. 

This project validated the use of thermal efficiency index (TEI) for evaluating feed efficiency in growing pigs. This study investigated the relationship between thermal efficiency and stress resilience. In a 2 x 2 design, weaner pigs were assessed for TEI, with high and low TEI animals selected; half of each group received a commercial supplement in water (DSS, designed to reduce stress) for 24h before and after stressful events, and half were treated as control. Pigs were challenged with a controlled handling and mixing stressor at 12 and 16 weeks respectively. Infrared temperature was evaluated before and after each stressor with additional salivary cortisol and thermal imaging measurements in the second replicate. TEI shows a consistent correlation with average daily gain, which indicates a valid metric for measuring pigs’ growth. Use of DSS in water significantly reduced lesion scores at mixing compared to the control and produced a greater change in TEI in response to handling and mixing stressors.  

Inefficient pig waste more energy

Feed efficiency is variable with ‘inefficient’ animals wasting more energy by giving off more heat than efficient animals, and/or absorbing less energy from feed and releasing unused nutrients to the environment. The thermal output of animals is thus a potentially useful measure for estimating feed efficiency. Infrared thermography can assess thermal output in real time and shows many other technical and practical advantages. The procedure is non-invasive and can be used to rank an animals’ efficiency in approximately 20 seconds. The technology has also been patented, beta site tested, and is now entering use in commercial facilities. Further work is needed to validate TEI as a tool in swine production, including for example knowledge on relationships between TEI and stress resilience, the effects of different diet formulations on TEI, heritability of TEI, as well as relationships with susceptibility to heat stress and pig temperament. The application of thermal profiles will be of particular benefit to genetic companies. By facilitating the early selection of pigs on the basis of efficiency, faster genetic progress can be achieved.

Because TEI can be measured in early life, the application of infrared technology and thermal profiles could also benefit pork producers. If young pigs can be sorted based on feed efficiency at the weaner or grower stage, diets can be prepared based on the different needs of each group. With thermal classification, each group of pigs would be provided a diet nutritionally tailored to better meet their needs, resulting in improved efficiency.

What we found

As the nature of TEI calculation considers body weight, we were not able to perfectly balance the body weight at entry. At weaning age, the greater feed efficiency of LOW animals resulted in higher body weights compared to HIGH animals. The average baseline weight for LOW pigs was almost 5kg heavier than the average for HIGH pigs (20.28 ±1.82 kg vs 15.61 ±1.43 kg, P < 0.001). Average weight at trial entry did not differ between dietary treatment groups. LOW pigs tended to have a higher ADG from 8-12 weeks. During Finisher 1, LOW pigs consumed more feed and had greater ADG with no difference in G:F. During Finisher 2, there was no difference in ADFI, ADG or G:F between TEI categories. The overall ADG throughout the grower-finisher stage was greater for LOW than HIGH pigs. LOW pigs had greater slaughter weight, and fat (mm). There was no effect of TEI on loin depth. 

During handling at 12 weeks, DSS tended to affect the change of TEI (∆TEI), with pigs given DSS showing greater change (Figure 1). In the mixing stressor at 16 weeks test, DSS pigs showed a greater ∆TEI than CTR pigs, with no effect of TEI category (Figure 2). Thermal efficiency and DSS treatment did not affect behaviour during handling. DSS treatment affected lesion scores at mixing: CTR animals received more head lesions and tended to have more mid-body lesions compared to DSS. TEI category tended to influence hind-end lesions; scores of HIGH pigs showed less change than LOW.

In terms of the relationship between thermal efficiency index and bodyweight, a linear correlation was detected. Initial TEI and bodyweight were negatively correlated, similarly at week 12, which means that pigs with lower TEI were consistently heavier. Interestingly, in week 12 after the handling stress, the correlation decreased, which suggests that pigs’ body temperature was indeed disrupted by the handling stress process. Similar results were found at week 16 before the mixing stress and after.

Implications

The findings based on thermal efficiency alone exhibit that TEI can be used to identify pigs with better performance in terms of weight gain and carcass yield. Based on data from the beginning of the trial, at week 12, and at slaughter, there was a negative correlation between TEI and bodyweight, with LOW pigs being heavier at each point. Both handling and mixing stress decreased the extent of this negative correlation, exhibiting the physiological influence of stress. 

This project is supported by the Saskatchewan Agriculture Development Fund