Researchers: M. E. Wastell, Gro Master Inc.; C. A. P. Garbossa, University of São Paulo; Ricardo Garcia, Purdue University; and A. P. Schinckel, Purdue University
Targeting heavier weights at market requires more room at the feeder for grow-finish. While previous research has focused on the number of pigs per feeder space, some recent research with Purdue University indicates that the type of feeder as well as floor space allowance may play an important part in increasing pig growth performance and gain efficiency.

Past research has only been done with dry feeders on the impact of the number of pigs per feeder space and has produced variable results, which researchers say could possibly be due to the different models of feeders and the different levels of feeder adjustment. Considering that feeder space per pig and pen floor space allowance per pig can affect pig growth performance, the objective of their research was to evaluate the effects of different feeder stocking density and pen stocking density on the growth performance of grow-finish pigs fed with wet/dry feeders.

The research facility
Conducted at a commercial research finishing barn located in southwest Minnesota the trial was held from October 2015 to September 2016. Double curtain-sided with totally slatted floors, the facility was environmentally controlled with sprinklers to reduce summertime heat stress and heaters for wintertime temperature control. Each building contained 44 pens. The pens had adjustable gating to provide the different floor space allowances, so each floor space allowance was arranged by moving the gates after measurement of the floor space.

The experimental treatments were designed as a two-by-three factorial arrangement (pen space of 0.65 or 0.78 m² per pig times 10, 13 or 16 pigs per feeder space). Each pen had an equal number of barrows and gilts, with 20, 26 and 32 pigs per pen for the 10, 13 and 16 pigs per feeder space pens, respectively. Each pen was equipped with one wet/dry, single-space, double-sided feeder, with a space of 37.5 cm of length and with one nipple drinker. The feed was delivered by a robotic feeding system, which recorded the daily individual pen feed additions.

Feeders and floor space
All pigs had ad libitum access to feed and water supply during the trial period. Pigs for the three replicates were fed with the same feeding program with a seven-phase corn-soybean meal base feed in mash form. The diets were formulated to achieve or exceed National Research Council (2012) requirements for grow-finish pigs.

Pigs were weighed by pen at the start of trial, at approximately every 21 days of the trial, and at the end of the trial to calculate average daily gain. All the feed placed in the feeders was weighed, and at the end of the trial, the remaining feed in the feeders was weighed to determine average daily feed intake and the gain-to-feed ratio.

To express floor space allowance, k-value was used, as it describes pen space as a function of effective pig space requirements (body weight^{0.67 kg}). The k-values were calculated using a formula reported by Whittemore (1998): space per pig (m²) = k times BW(kg)^0.67. According to Gonyou et al. (2006), a k-value of 0.0336 is required for maximal feed intake and ADG for grow-finish pigs with fully slatted flooring.

Pig performance results
No interactions (P value > 0.05) of floor space allowance with pigs per feeder were observed. Pigs with less floor space allowance had reduced body weight (128.8 vs. 129.5 kg, P = 0.026), average daily gain (1.00 versus 1.02 kg/day, P = 0.002) and average daily feed intake (2.52 vs. 2.61 kg/day, P < 0.001). However, G:F was improved (0.402 vs. 0.397, P = 0.039), with less floor space allowance per pig.

Increased pigs per feeder space reduced final BW (129.7, 129.4, 128.4 kg, linear; P = 0.001). However, ADG had a quadratic relationship (P = 0.005) with pigs per feeder space with means of 1.03, 1.01 and 1.01 kg/d for 10, 13 and 16 pigs per feeder space, respectively.

Overall, ADFI had a quadratic relationship (P < 0.0001) with number of pigs per feeder space with means of 2.62, 2.52 and 2.55 kg/d for 10, 13 and 16 pigs per feeder space, respectively. Gain efficiency had a quadratic relationship (P = 0.005) with number of pigs per feeder space with means of 0.395, 0.404 and 0.400 for 10, 13 and 16 pigs per feeder space, respectively. A subsequent economic analysis indicated 13 to 14 pigs per feeder space was optimal.

Contradictory conclusion
The results of this trial contradict some past research that found G:F was unchanged (Brumm and Miller, 1996; Gonyou and Stricklin 1998; Jensen et al., 2012; Thomas et al., 2017) or decreased (Street and Gonyou, 2008; Flohr et al., 2016) with decreased floor space allowance per pig. In this trial, G:F was greater for pigs with less floor space allowance. This observation is in agreement with a meta-analysis (Averós et al., 2012) that suggested that the pig floor space required for maximal G:F is reduced if the pigs are housed on fully slatted floors compared to pens with nonslatted floors. Despite the reduced ADG and final BW of pigs with the floor space allowance of 0.65 m², the pigs had better G:F for the overall grow-finish period.

These findings are important considering that the final BW difference of 0.7 kg represents less than one day of ADG for the overall period; however, the difference on ADFI represents 9.00 kg of feed for the overall period of 100 days and is economically more representative.

In conclusion, a floor space allowance of 0.65 m2 per pig in the grow-finish period reduced ADFI and ADG. Thirteen pigs per feeder space resulted in overall similar performance, with slightly reduced ADG and improved gain efficiency, than 10 pigs per feed space when fed with wet/dry feeders. Bottom line: A reduced cost of feeders means reduced equipment costs to producers.

For more information, contact Schinkel.