32 2013 North Dakota Beef Report

Pancreatic enzyme activity in high- vs. low-efficiency steersF.E. Doscher1, L.D. Prezotto1, S.I. Paisley2, A.M. Meyer2 and K.C. Swanson2

1Department of Animal Science, University of Wyoming 2Department of Animal Science, NDSU

The objective of this study was to determine if pancreatic mass or pancreatic digestive enzyme activity differs between steers of high and low efficiency. We found a trend toward a larger pancreas mass in high-efficiency steers. However, pancreatic digestive enzymes were not impacted by feed efficiency classification.

SummaryHereford-Angus crossbred

steers (n = 59) were fed a common finishing diet (11.4 percent crude protein [CP], 4.41 megacalories of net energy for maintenance per pound [Mcal NEm/lb], 2.98 Mcal of net energy for gain per pound [NEg/lb]) for 57 days using the GrowSafe feed intake system. Re-sidual feed intake (RFI), a measure of feed efficiency, was determined for all steers with at least 0.4 inch of 12th rib fat thickness at the end of the feed intake test (n = 40). The 20 percent most efficient (n = 8) and 20 percent least efficient (n = 8) steers then were selected and randomly allocated to two slaughter dates five and seven days after the conclusion of the feeding trial. At slaughter, the pancreas was removed, trimmed of fat and weighed. Samples of each pancreas were flash-frozen immedi-ately and stored at minus 112 F for further analysis of protein content and "-amylase and trypsin activity. We found a trend (P < 0.10) toward high-efficiency (low-RFI) steers having greater pancreatic weight (ounces) per pound of body weight. No significant differences were observed (P > 0.2) between high- and low-efficiency steers for protein concentration or pancreatic "-amy-lase and trypsin activity. These data

indicate that more efficient steers may have a trend for increased pan-creatic mass without an alteration in pancreatic digestive enzyme activity.

IntroductionFeed efficiency holds great value

in livestock production. Cattle that are more efficient require less feed for productive purposes such as growth. Residual feed intake (RFI) is calculated as the difference between the actual feed intake of an animal and its expected feed intake based on the animal’s size, maintenance requirements and growth during a specified period of time (Richardson et. al., 2001).

Herd and Arthur (2008) outlined five areas influencing RFI. These ar-eas are as follows: processes related to the ingestion of feed, digestion and absorption of nutrients, mainte-nance requirements, physical activ-ity and thermoregulation. Cattle with a lower RFI are able to grow as rapidly as animals with greater intakes while consuming less feed, thus reducing total feed costs.

Research has suggested that us-ing selective breeding to obtain cat-tle with lower RFIs in future genera-tions (Herd et. al., 1998) is possible. More information is needed to better understand the underlying mecha-nisms controlling feed efficiency to understand the impacts that this selection has on livestock and to al-low for the creation of management

strategies to improve efficiency.The pancreas is responsible for

the secretion of digestive enzymes such as "-amylase and trypsin. These enzymes assist in the break-down of nutrients in the small intestine. In the small intestine, "-amylase initiates the digestion of starch to simple sugars, which are absorbed by the small intestine, whereas trypsin initiates the diges-tion of proteins into peptides and amino acids, which are absorbed in the small intestine. The ability of cattle to grow and develop with lower input may be associated with improved function of the animal’s organs (Ferrell and Jenkins, 1985) such as the pancreas.

The objective of this study was to determine the relationship between improved efficiency and pancreatic function as related to feed digestion. We hoped to estab-lish whether a correlation existed between greater efficiency and the mass of the pancreas or the secretion of its enzymes. We hypothesize that as an animal becomes more efficient, the amount of pancreatic digestive enzymes will increase to support metabolic demands.

Experimental ProceduresIn March 2012 at approximately

12 months of age and weighing roughly 1,016 ± 10 pounds, 59 Hereford-Angus crossbred steers were trained to use the GrowSafe feed intake system at the University of Wyoming Sustainable Agricul-ture Research and Extension Center (SAREC) in Lingle, Wyo. They were fed a common corn-based finish-ing diet (11.4 percent CP, 4.41 Mcal NEm/lb, 2.98 Mcal NE/lb; dry-mat-ter [DM] basis) for 57 days.

At the end of the feed intake

2013 North Dakota Beef Report 33

period, RFI was calculated for all steers with at least 0.4 inch of fat thickness (n = 40) by subtracting the expected feed intake from the actual feed intake. Expected feed intake was determined by regress-ing average daily gain (ADG) and metabolic midweight on actual feed intake. The 20 percent most efficient (n = 8) and 20 percent least efficient (n = 8) steers then were selected and randomly allocated to two slaughter dates five and seven days after the end of the feed intake test.

At slaughter, the pancreas was removed, trimmed of fat and weighed. Samples from each animal were frozen immediately on dry ice and stored at minus 112 F until fur-ther analysis. Trypsin and "-amylase activity were measured kinetically on a microplate reader. Data were analyzed using the PROC MIXED procedure of SAS with RFI class (high vs. low efficiency) as a fixed effect in the model. Enzyme activity is reported as units of activity per

ounce of pancreatic tissue (U/oz), total units of pancreatic activity (U/pancreas) and total units of activity relative to maternal body weight (U/lb BW).

Results and DiscussionIn this study, no differences (P

= 0.84) in the final body weights of steers were observed (Table 1). We found a trend (P < 0.10) for pancreatic mass, relative to body weight, to be greater in the low-RFI (high-efficiency) steers. We found no differences in protein concentration or activity of pancreatic enzymes ("-amylase and trypsin) among steers differing in feed efficiency (Table 1).

Our results agree with those of Mader et al. (2009), who found no significant correlations among performance measures and pancre-atic mass or enzyme activity. Taken together, these results suggest that differences in feed efficiency be-tween animals may not be related

to digestive enzyme concentrations in the pancreas. Further work is necessary to determine how, if at all, improved efficiency could be related to digestive function.

AcknowledgmentsThe authors thank the employ-

ees of the University of Wyoming Sustainable Agriculture Research and Extension Center and Meat Laboratory and also several Univer-sity of Wyoming Animal Sciences faculty, staff, and graduate and undergraduate students for their as-sistance with animal husbandry and data collection.

Literature CitedFerrell, C.L., and T.G. Jenkins. 1985. Cow

type and the nutritional environment: Nutritional aspects. J. Anim. Sci. 61:725−741.

Herd, M., and P.F. Arthur. 2009. Physi-ological basis for residual feed intake. J. Anim. Sci. 87(E.Suppl.):E64-E71.

Herd, R.M., E.C. Richardson, R.S. Hegar-ty, R.T. Woodgate, J.A. Archer and P.F. Arthur. 1998. Pasture intake by high versus low net feed efficient Angus cows. Anim. Prod. Aust. 22:137–140.

Mader C.J, Y.R. Montanholi, Y.T. Wang, S.P. Miller, I.B. Mandell, B.W. Mc-Bride, K.C. Swanson. 2009. Relation-ships among measures of growth performance and efficiency with carcass traits, visceral organ mass, and pancreatic digestive enzymes in feedlot cattle. J. Anim. Sci. 87:1548-57.

Richardson, E.C., R.M. Herd, V.H. Oddy, J.M. Thomspon, J.A. Archer and P.F. Arthur. 2001. Body composition and implications for heat production of Angus steer progeny of parents selected for and against residual feed intake. Aust. J. Exp. Agric. 41:1065–1072.

Table 1. Influence of RFI classification on pancreatic mass and digestive enzyme activities.

Treatment

Item aHRFI bLRFI SEM P-Value

Final BW, lb. 1,215 1,226 39.9 0.84Pancreas wt., oz. 18.2 21.2 1.55 0.21Pancreas/BW, oz./lb. 0.02 0.02 0.001 0.10Pancreatic protein oz./lb. 1.99 2.24 0.18 0.31 oz./pancreas 0.09 0.11 0.01 0.17 oz./lb. of BW 0.002 0.01 0.0002 0.11Pancreatic "-amylase U/oz. 2.47 4.09 0.85 0.22 KU/pancreas 37.7 70.4 14.80 0.15 U/lb. of BW 148 273 55.3 0.15 U/oz. protein 9.42 17.1 3.34 0.14Pancreatic trypsin U/oz. 0.03 0.03 0.01 0.54 U/pancreas 487 448 98.3 0.79 U/lb. of BW 3.37 2.76 0.6 0.48 U/oz. protein 0.25 0.18 0.04 0.24

aHigh Residual Feed Intake = Low Efficiency Steers bLow Residual Feed Intake = High Efficiency Steers