Summary and Implications

The variation in backfat of commodity pork has declined to the point some major packers are no longer measuring backfat depth, according to Matt Swaneck and colleagues a tIowa State University.

From their previous research with Berkshire pigs, they found a large amount of variation in backfat and loin eye area (LEA) still existed, especially between barrows and gilts. In previous research, barrows average one inch backfat depth around 210 pounds whereas gilts did not achieve one inch until 260 pounds. This may be a meat quality issue for gilts marketed less than 260 pounds.

The objective of these trials was to replicate our previous study and to determine whether these differences persisted within a different set of Berkshire pigs under the same nutritional regimen. Understanding how feed programmes and growth rates affect lean and fat deposition rates is a critical aspect to these niche programmes in order to maintain consistency and quality of the Berkshire pork products marketed.

Overall, barrows averaged an inch of backfat between 230 and 250 lb body weight whereas gilts average backfat was 0.90 inches at 269 pounds market weight. Only a 30 per cent of the gilts within these two groups had over one inch backfat at market.

These differences are crucial when selecting animals for market to achieve the highest desirability in meat quality within the Berkshire marketing system. These differences between barrows and gilts indicate it may be more critical that each are fed differently than in commodity pork production systems.

Introduction

The niche marketing of Berkshire pigs continues to grow in Iowa and the United States as the demand for high quality pork increases through the market chains. As the number of producers increases to meet the demand for Berkshire pork, concerns about maintaining consistency and eating quality are growing. There is limited information available to characterise the backfat changes or percentage of lean within the Berkshire programmes and consequently, no benchmarks exist for producers or guidelines for quality control of their products.

This paper is the summary of the second phase to the Berkshire growth trials conducted at the ISU Western Research Farm, Castana, Iowa.

As Berkshires have a reputation of being fatter and less efficient in feed conversion, it is important that to understand how these animals deposit fat and lean as they reach market weight. Characterising compositional changes in backfat and muscle expression for purebred Berkshire pigs will enable more accurate feed formulation for meat quantity, quality and consistency.

The purpose of this project is to characterise typical backfat, LEA and percentage of lean for purebred Berkshire pigs in bedded hoop barns in Iowa.

Materials and Methods

This study was conducted at the Iowa State University Western Research Farm.

Two distinct trials, winter (Trial 3) and summer (Trial 4), were conducted in order to include the environmental extremes of Iowa’s climate. In each trial, 36 Berkshire feeder pigs (18 gilts and 18 barrows) were purchased from the same genetic source as our first set of trials and housed in bedded mini-hoop barns.

The targeted grow-out was from 50 to 270 pounds of live weight. Pigs were allotted by sex and weight (light, medium and heavy) of six pigs per pens; two pens per hoop. Gilts and barrows of similar weights were housed in one of three mini hoops which were divided into two pens of six pigs or 12 pigs per hoop.

Pigs were fed ad libitum a six-phase feeding programme of corn-soybean meal based diets that met or exceeded amino acid requirements. Pigs were weighed (BWT) approximately every 21 days. Ultrasonic scans for 10th backfat depth and LEA began at between 80 and 100 pounds. Thereafter, scans were recorded approximately every six weeks with a minimum of four scans per pen. As pens neared the target market weight of 270±5 lb, pigs were scanned at each weigh period. Ultrasonic percent lean was calculated by the equation:

• % Lean = (0.833*gender-16.498*Backfat + 5.425*LEA +0.291*BWt-0.534) / BWt ; (gender: barrows=1; gilts=2)

Results and Discussion

Summarised in the table below are the initial and final pig weights, ultrasonic scans of backfat and (LEA), and the calculated carcass percent lean (74 per cent yield). Average trial weights were 92 and 83 pounds for the first scans and averaged 270 and 273 pounds for the off-test weights for trials 3 and 4, respectively.

Table 1. Live ultrasonic measurements and calculated percent lean of Berkshire pigs
		Bodyweight (lb)		Backfat (inches)		Loin eye area (in2)
Trial	Wt-Sex	1st scan wt.	Final	Initial	Final	Initial	Final	Carcass % lean**
3	Lt-G	70	256	0.28	0.78	2.10	6.56	51.8
	Lt-B	86	271	0.38	1.41	2.30	5.82	44.1
	Med-G	79	273	0.30	0.77	2.29	6.85	52.1
	Med-B	101	272	0.46	1.31	2.86	6.67	47.6
	Hy-G	101	274	0.40	1.04	2.60	6.33	48.9
	Hy-B	113	272	0.48	1.20	3.02	6.54	48.3
4	Lt-G	74	270	0.33	0.88	2.08	6.73	51.1
	Lt-B	68	275	0.32	1.24	1.95	6.20	46.3
	Med-G	81	269	0.36	0.96	2.44	6.67	50.3
	Med-B	85	279	0.40	1.14	2.35	6.23	47.1
	Hy-G	87	271	0.37	0.99	2.50	6.33	48.9
	Hy-B	94	274	0.40	1.01	2.95	6.96	50.2
3	G	83	267	0.33	0.86	2.33	6.58	50.9
	B	100	272	0.44	1.31	2.72	6.34	46.7
4	G	80	270	0.35	0.94	2.34	6.58	50.1
	B	83	276	0.37	1.13	2.42	6.46	47.9
Overall	Trial 3	92	270	0.39	1.09	2.53	6.46	48.8
	Trial 4	81	273	0.36	1.04	2.38	6.52	49.0
	Gilts	82	269	0.34	0.90	2.34	6.58	50.5
	Barrows	91	274	0.41	1.22	2.57	6.40	47.3
	All pigs	87	271	0.37	1.06	2.45	6.49	48.9
* Lt=light; Md=medium, Hy=heavy weight; G=gilts; B=barrows. ** %Lean = (0.833*gender - 16.498*Backfat + 5.425*LEA + 0.291*BWt-0.534) / BWt * 74%

As expected, gilts averaged less backfat than barrows throughout the two trials; 0.34 versus 0.41 inches at first scan and 0.90 versus 1.22 inches for the final scan, for gilts versus barrows, respectively.

However, gilts had smaller LEA (2.37 versus 2.54 square inches) than barrows at first scanning but were larger (6.58 versus 6.40 square inches) than barrows for the final scans.

Berkshire hogs are not as lean as commodity lines but the relative difference between barrows and gilts in percent lean was consistent. Overall, gilts were leaner than barrows at 50.5 per cent versus 47.3 per cent, respectively.

The authors of this paper - published in Iowa State University Animal Industry Report 2014 - were Matt Swantek (Swine Field Extension Specialist), Wayne Roush (Farm Superintendent), David Stender (Swine Field Extension Specialist), John Mabry (Professor) and Mark Honeyman (Professor), Department of Animal Science.

Acknowledgements: The authors gratefully acknowledge Don Hadden, Harry Riesberg and Jacob Clemon for their assistance in the feeding, weighing and the care and well-being of the pigs during these trials, and Dallas MacDermot (MacScan) for ultrasonic scanning of the pigs.

June 2014