2011 Carcass Comparison Study
A preliminary comparision of pen-fed vs. pasture-raised goats
A carcass comparison study was conducted in association with the 2011 Western Maryland Pasture-Based Meat Goat Performance Test. The carcasses from nine goats in the pasture test were compared to the carcasses from nine genetically-similar goats that were pen-fed a diet of hay and grain.
Consigners to the test were asked to provide goats of similar genetics for pen-feeding and carcass evaluation. For each goat in the pen that was harvested, there was another goat from the same consigner in the pasture test that was harvested for data collection.
The pasture-raised goats (n=9) consumed a pasture-only diet while on test. They were rotationally grazed among six 2-acre paddocks, composed of various cool and warm season grasses. There was always ample forage, but the quality of the forage was not evaluated. The average daily gain of the pasture-raised goats was 0.128 lbs. per day (June 10-September 15).
The pen-fed goats (n=9) were housed in a 16 ft2 zero-grazing pen and given unlimited access to grass hay via a 4-foot, double-sided hay rack. They were hand-fed grain (ADM Goat Power™) once daily in poly troughs that were hung on the side of the fence. They were fed the amount of grain they could consume in 20 minutes, very little at the start of the test, but almost 1.7 lbs per head by the end of the test. Their average daily gain was 0.232 lbs. per day (June 10- September 15).
Both groups of goats had free choice access to minerals: SweetLix 16:8 Meat Maker® with Rumensin®. After consuming their respective diets for 112 days, the goats were weighed and transported 37 miles to a custom-exempt slaughterhouse (Country Foods, Waynesboro, PA) for same day slaughter. The carcasses were weighed, deboned, and measured six days later.
Weights
According to statistical analysis, there was no difference in live weight (LW) between the two groups of goats. Live weights ranged from 42 to 86 lbs. and averaged 60.3 +11.1 lbs. The lack of statistical significance is probably due to the fact that the pen-fed goats had a wider variation in weight: 42-86 vs. 48-65 lbs.
Hot carcass weights (HCW) were determined immediately after slaughter. The pen-fed goats tended (P<0.065) to have heavier hot carcass weights: 28.4 vs. 22.6 lbs. In the pasture group, HCW ranged from 17.5 to 27.5 lbs. and averaged 22.6 +3.5 lbs. For the pen-fed goats, HCW ranged from 16 to 40 lbs. and averaged 28.4 +8.1 lbs. Again, the wider variation in weights among the pen-fed goats probably resulted in the lack of statistical significance.
After chilling for six days, cold carcass weights (CCW) were determined. The cold carcass weights of the pen-fed goats were heavier than the cold carcass weights of the pasture-raised goats: 27.1 vs. 20.6 lbs. CCW of the pastured-raised goats ranged from 15.5 to 25 lbs. and averaged 20.6 +3.2 lbs. For the pen-fed goats, CCW ranged from 14 to 39.5 lbs. and averaged 27.1 +8.2.5 lbs. Statistical analysis showed the difference in cold carcass weight to be significant.
Dressing percentage
Dressing percentage is affected by many different factors, including fat, muscle, gut fill, and transport shrinkage. It is calculated by dividing the hot carcass weight (HCW) by the live weight (LW).
Dressing percentage was higher for the pen-fed goats than the pasture-raised goats: 44.4 vs. 39.4 %. For the pasture test goats, dressing percentage ranged from 35.8 to 44.4 percent and averaged 39.4 +3.4 percent. For the pen-fed goats, dressing percentage ranged from 36.5 to 50 percent and averaged 44.4 +4.7 percent. Statistical analysis showed the difference in dressing percentage to be significant (P<0.02)
Pasture-raised
Pen-fed
In past years, the goats were weighed immediately before slaughter. This year, the goats were weighed prior to transport, which at least partially accounts for the lower dressing percentages in the pasture-raised goats.
Rib eye area
The longisimus dorsi muscle was exposed between the 12th and 13th rib so that rib eye area could be measured a plastic grid, with 20 dots being equal to 1 square inch of muscle. Rib eye area was also estimated on September 1 via ultrasound.
According to statistical analysis, there was not a signficant difference in rib eye area in the two groups of goats. For all the goats, rib eye area ranged from 0.80 to 2.15 in2 and averaged 1.41 +0.42 in2. Ultrasound measurements of rib eye were less than the carcass measurements, and the difference was statistically significant (P<0.02).
The goat with the largest rib eye area was a percentage Kiko consigned by Ron & Lolli Allen (TN). The 74-lb. buck had an impressive 2.15 in2 rib eye. Allen's other pen-fed buck, another percentage Kiko had a 2.10 in2 rib eye, as did a pen-fed Spanish buck consigned by Karen Cooper (KY). The largest rib eye (1.75 in2) amongst the pasture-raised goats was from the Myotonic buck consigned by Whitmore Farm (MD).
Fat
Kidney and heart fat (KH) was removed from each carcass and weighed. Percent KH was determined by dividing the weight of the fat by the cold carcass weight of each goat. The pasture-raised goats had less KH than the pen-fed goats: 1.4 vs. 2.6 percent. KH ranged from 1.10 to 1.84 percent in the pasture-raised goats and averaged 1.4 +0.02 percent. There was more variation in the amount of KH in the pen-fed goats. Percent KH ranged from 1.48 to 4.11 percent and averaged 2.6 +0.08 percent. Statistical analysis showed the different in kidney and heart fat to be significant (P<0.0005).
As back fat is negligible on goats unless they are fed to a higher degree of finish, body wall thickness (BWT) was measured instead and used as an indicator of fat cover. The pen-fed goats had greater body wall thickness than the pasture-raised goats: 0.24 vs. 0.16 inches. In the pen-fed goats, BWT ranged from 0 to 0.30 inches and averaged 0.24 +0.1 inches. The BWT of the pasture-raised goats ranged from 0.10 to 0.20 inches and averaged 0.16 +0.05 inches. According to statistical analysis, the difference in body wall thickness was significant (P<0.04).
Carcass percentages
The carcasses were deboned in order to separate the lean from the bone and fat. Percent bone, fat, and lean were calculated by dividing the weight of the bone, fat, and lean by the cold carcass weight of each goat. According to statistical analysis, there was no difference in the percentage of bone in the pasture-raised vs. the pen-fed goats. Percent bone ranged from 32.5 to 47.2 percent.
KH fat was added to the fat trimmings to determine the amount of fat in the carcass. The pen-fed goats had twice as much carcass fat as the goats from the pasture test: 4.3 vs. 2.1 percent. %F ranged from 1.8 to 3.4 percent and averaged 2.1 +0.06 percent in the pasture-raised goats. In the pen-fed goats, %F ranged from 1.74 to 6.03 percent and averaged 4.3 +0.15 percent. Statistical analysis determined the differences in fat percentage to be significant (P<0.008).
In contrast, differences in percentage lean (%L) were not determined to be statistically different. For all goats, %L ranged from 50.1 to 64.7 percent. Yield was determined by dividing the pounds of edible, boneless meat (lean) by the live weight of the goat. The pen-fed goats had a higher carcass yield than the pasture-raised goats: 24.5 vs. 19.8 percent. For the pasture-raised goats, carcass yield ranged from 16.2 to 24.8 percent and averaged 19.8 +2.9 percent.
For the pen-fed goats, carcass yield ranged from 17.1 to 29.8 percent and averaged 24.5 +4.5 percent. According to statistical analysis, the differences in yield were signficiant (P<.017). In both groups, the highest yielding goat was a Myotonic consigned by Whitmore Farm. The Myotonic breed is known for having a superior meat-to-bone ratio. While the Myotonic carcasses were shorter, they showed superior muscle conformation, especially in the leg.
Meat quality
A sample of the longissimus dorsi muscle was collected from each carcass. The samples were analyzed by Dr. Henry Zerby's meat lab at Ohio State University.
There was no difference in the percentage of protein or intramuscular fat in the samples from the pen vs. pasture-fed goats. The samples contained an average of 23.3 percent protein and 1.03 percent intramuscular fat.
The fatty acid data is much more complex and harder to interpret, as the percentages of 28 different fatty acids were compared. Statistical differences were detected in 8 of the 28 fatty acids that were measured.
The following table gives the number of grams of each fatty acid per 100 g of fat. The final column in the table indicates whether or not the differences measured were statistically significant. The meat from the pen-fed goats had a higher portion of mono-unsaturated fat (MUFA), whereas the meat from the pasture-raised goats had more poly-unsaturated (PUFA) and saturated fat (SFA). It is not known if any of these differences are relevant to human health.
Conclusion
While these data show that pen-feeding can improve carcass yield without affecting fatty acid profile, the economics of pen-feeding will vary by operation. Next year, a similar study will be conducted to evaluate carcass differences, as well as the economics of pasture vs. pen-feedng of meat goats.
For information about the goat carcass evaluation and/or Western Maryland Pasture-Based Meat Goat Performance Test, contact Susan Schoenian at (301) 432-2767 ext. 343 or sschoen@umd.edu. Information can also be found on the blog at http://mdgoattest.blogspot.com.