Effect of the available space in the fattening pens on growth and carcass

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Effects of space allocation on finishing pig growth performance and carcass characteristics L. L. Thomas, R. D. Goodband, J. C. Woodworth, M. D. Tokach, J. M. DeRouchey, and S. S. Dritz. Transl. Anim. Sci. 2017.1:351–357. doi:10.2527/tas2017.0042
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Comment

There are several articles on pig density in the fattening stage, but what's interesting about this one is that it fulfills some important aspects: a) It keeps the group size constant (9 animals), whilst in most of the articles, the number of pigs housed in the same area is changed, so the result is a mixed effect of space allocation and group size; b) the authors claim that there are no space restrictions regarding the feed troughs and the drinkers; and c) the experiments were carried out in thermoneutral conditions, guaranteeing good comfort conditions. Due to this, we believe that the conclusions reached are very solid.

Animal density is a key factor in the fattening stage, besides being one of the most valued criteria by the consumers, as they associate greater welfare with greater space availability. In the last 20 years, the average weight of the pigs sent to the abattoir in the USA has increased (from 116 to 129 kg) without significant modifications in the fattening rooms. Something similar happens when, without variations in slaughter weight, the sows' productivity increases (pigs weaned/sow/year), as the batches of weaned pigs are larger, and therefore overpopulation or overcrowding problems appear in the final phases of the fattening stage. On the other hand, in warm countries like Spain, it is advisable to work with lower densities in the hot seasons to avoid heat stress incidents. Under these conditions, a pig takes up more space to rest in order to facilitate heat loss by conduction. As pigs remain more than 80% of the time laying down, ensuring that they have enough space available optimises their welfare. The EU animal welfare regulations demand a minimum space allocation of 0.65 m² per a 100 kg pig (equivalent to a “K” value of 0.030; "space allocation" = K*(LW)^0.67), although in some countries higher values are recommended.

Experiment

The authors used 405 pigs grouped in 36 pens with 9 animals each, and two equivalent experiments comparable to two production batches. Three different space allocations were tested (0.65; 0.74 and 0.84 m² per pig) to assess the maximum body weight compatible with the best production results and the possible effect on carcass quality. The feed trough space was 7.9 linear cm/pig with bowl drinker, completely slatted floor and feed always ad libitum.

Results

The results do not show significant differences between the treatments in terms of carcass yield, backfat thickness or eye muscle depth. The authors show that the main effect of space restriction is on feed consumption followed by growth, but as opposed to other previous studies, the feed conversion ratio (or feed efficiency) is not necessarily affected. They also point out that the liveweight from which feed consumption is affected would be 120, 102 and 83 kg for space allocations of 0.84, 0.74 and 0.65 m²/pig. This result produces a higher “K” value of between 0.0334 and 0.0338. On the other hand, according to the authors, it is unknown if a space allocation exceeding 0.84 m² would improve the production indexes.

Conclusions and practical implications

In conclusion, the space allocation needed to optimise the performance of pigs housed in small groups and thermoneutral conditions and that are slaughtered at 105 kg LW would be 0.76 m2/pig. A space allocation of 0.65 m2/pig only ensures an optimal feed intake until 83 kg LW in the best of cases, if all the rest of the production limiting factors are under control. The main limiting factor of these results is that they don't allow to extrapolate the conclusion to large groups of pigs, although it points out that, in general, it is necessary to provide more space to the pigs at the end of the fattening stage.

Summary of the commented article Effects of space allocation on finishing pig growth performance and carcass characteristics L. L. Thomas, R. D. Goodband, J. C. Woodworth, M. D. Tokach, J. M. DeRouchey, and S. S. Dritz. Transl. Anim. Sci. 2017.1:351–357. doi:10.2527/tas2017.0042 Background and methods: A total of 405 pigs (PIC 327 × 1,050) were used in 2 experiments (Exp. 1, initially 66.1 ± 1.8 kg BW, Exp. 2 initially 60.8 ± 2.5 kg BW) to examine the effects of space allocation on finishing pig growth performance and carcass characteristics. Pigs were randomly allotted to pens on entry into the finishing facility. Pens of pigs were balanced by initial BW and randomly allotted to 1 of 3 treatments with either 7 or 8 replications per treatment (Exp.1 and 2, respectively). There were 9 pigs per pen and gates were adjusted to provide 0.84, 0.74, or 0.65 m2 per pig. Each pen was equipped with a dry single-sided feeder with two 35.6 cm × 11.4 cm (length × width) feeder spaces and a cup waterer. Results: In both experiments, as space allocation decreased, overall ADG and ADFI decreased (linear, P < 0.019) with no evidence for differences in G:F. In Exp. 2, there was marginal evidence for a linear improvement (P = 0.061) in G:F as space allocation decreased from d 42 to 56. Final BW was 3.8 and 5.3 kg greater (linear, P ≤ 0.005) in Exp. 1 and 2, respectively, when comparing the 0.65 to the 0.84 m2 per pig space allocation treatments. Using a predicted k-value of 0.0336, ADFI and, subsequently, ADG should have begun to decrease when pigs reached 121.2, 101.7, and 83.3 kg at 0.84, 0.74, or 0.65 m2 per pig, respectively. In Exp. 1, we found marginal evidence for a reduction in ADFI as space allocation decreased starting at a mean BW of 80.3 kg (d 14; linear, P = 0.072). In Exp. 2, ADFI and consequently ADG decreased linearly (P < 0.029) starting at a mean BW of 74 kg, as space allocation decreased, before pigs reached the k-value that should have influenced performance. It is unknown if growth performance was impacted for the 0.84 m2 treatment group as this was the greatest space allocation treatment. Overall, these studies indicate that decreasing space allocation resulted in poorer ADG driven by a reduction in ADFI. The data suggests that the accepted k-value of 0.0336 might underestimate the impact of space restriction on finishing pig ADG and ADFI. Conclusion: Our trial was successful in determining the effects of space allocation on pig performance without affecting the results by restricting feeder space per pig. The differences in trial performance compared with expected outcomes from published reviews may have been attributable to group size, behavior, or other physiological variables. It is unknown whether these variables contributed to the negative effects on performance as space allocation decreased.