Animal Sciences Research and Reviews

Special Circular 156

Effects of Endogenous Cholecystokinin on Feed Intake in Dairy Heifers Fed High Fat Diets

B.R. Choi^*, D.L. Palmquist^*, and M.S. Allen^+
*Department of Animal Sciences, and ⁺Department of Animal Science, Michigan State University

Summary

Feeding fat depresses dry matter intake and increases plasma CCK, a potent satiety hormone, in dairy cows. The hypothesis that blocking the satiety effect of endogenous CCK restores feed intake of dairy cattle fed fat was tested. Four non-pregnant Holstein heifers were used in a cross-over design and fed low fat (LF, 2.7% fatty acids) or high fat (HF, 10.3% fatty acids) diets with two 14-day feeding periods. Half the animals were fed each diet in period 1, and diets were reversed in period 2. From days 9 to 12 of each period, either the CCK receptor antagonist (MK-329) or its vehicle was injected into two animals in each diet group at 2 hours postfeeding. Total dry matter intake for 24 hours was decreased by HF but not influenced by injections. The MK-329 injection, however, increased the amount of dry matter eaten during the first 2 hours by 96% over the control injection in the HF group (1.65 vs 0.84 pounds). Plasma insulin was lowered by HF pre- and postinjection but not influenced by MK-329. Plasma pancreatic polypeptide was increased by HF at 2 hours postfeeding but decreased by MK-329 at 2 hours postinjection. Plasma fatty acid and glucose concentrations were influenced by neither diet nor injections. The HF diet increased plasma triglycerides before injection, whereas triglycerides were decreased by MK-329 at 2 hours postinjection. Endogenous CCK was involved in short-term regulation of feed intake in dairy cattle fed fat under circumstances of the study. Also, CCK stimulated pancreatic polypeptide release, but it did not increase insulin. This is the first information on response of feed intake to a CCK antagonist in dairy cattle.

Introduction

Feeding high fat diets often decreases dry matter intake by dairy cows; decreased intake may be mediated by satiety hormones secreted in response to the presence of dietary fat in the intestine. Cows fed high fat diets had higher plasma cholecystokinin (CCK) and pancreatic polypeptide but had lower plasma insulin concentrations when compared with control cows (Choi and Palmquist, 1995). Cholecystokinin is a potent satiety hormone in sheep (Baile and Della-Fera, 1981) and in non-ruminants (Reidelberger, 1994). It is unknown, however, whether increased endogenous CCK is a causative factor in the fat-induced depression of feed intake in dairy cattle.

Cholecystokinin has been reported to be a secretagogue of insulin in sheep (Mineo et al., 1995) and pancreatic polypeptide in nonruminants (Alder et al., 1990). The direct effect of endogenous CCK on plasma insulin and pancreatic polypeptide is yet to be shown in dairy cattle.

The objective of this study was to investigate the effects of a non-peptide CCK type A (CCK_A) receptor antagonist, MK-329, on dry matter intake and plasma concentrations of metabolites, insulin, and pancreatic polypeptide in dairy heifers fed low or high fat diets.

Materials and Methods

Four nonpregnant and nonlactating dairy heifers averaging 1370+108 pounds body weight were used in a cross-over design using a 2 x 2 factorial arrangement of treatments with two 14-day feeding periods. Factors were diet (low vs high fat) and injection (MK-329 vs vehicle). Heifers were fed a totally mixed ration (TMR) of corn silage, cracked corn, soybean meal, and a vitamin and mineral mixture for ad libitum intake once daily (Table 1). A ruminally-inert fat (Energy Booster 100^®, Milk Specialties, Inc., Dundee, IL) isoenergetically replaced corn of the high fat TMR. Half the heifers were fed each diet in period 1, and diets were reversed in period 2.

At 2 hours after feeding on days 9 and 11, either MK-329 or the same volume of vehicle was injected through the jugular catheter into two animals in each diet group. Injections were reversed on days 10 and 12.

Blood plasma samples were analyzed for non-esterified fatty acids, triglyceride, glucose, insulin, and pancreatic polypeptide. Cumulative dry matter intake was measured continuously for 24 hours after feeding with a computer data acquisition system. Quantities of dry matter consumed after injection, recorded at 2, 4, 10, and 22 hours, were analyzed statistically. Quantities of dry matter consumed per given time and blood measures taken over time were analyzed by repeated measures. Diet, period, animal, and the 3-way interaction of diet, period, and animal were main plot factors, and injection and diet by injection interaction were the subplots in the statistical analysis. Protocols were reviewed and approved by the Michigan State University Animal Care and Use Committee.

Table 1. Feed ingredients and nutrient composition of diets.
Ingredients	Low fat	High fat
	(% of DM)
Corn silage	63.8	65.2
Cracked corn	15.5	3.6
Soybean meal	15.3	17.0
Prilled fat1	. . .	8.1
Sodium bicarbonate	0.8	0.8
Limestone	. . .	0.7
Vitamin and mineral mixture2	4.6	4.6
Nutrient composition
Crude protein	14.14	14.15
NDF3	34.75	34.02
Total fatty acids	2.67	10.27
1 Energy Booster® 100 (100% unesterified fatty acids containing: 16:0, 41.6%; 18:0, 44.5%; 18:1, 5.5%), marketed by Milk Specialties Co., Dundee, IL. 2 Contained 13.5% Ca, 2.7% P, 2.0% Mg, 0.15% K, 6.4% Na, 5.7% Cl, 1.1% S, 3.2 ppm Co, 188 ppm Mn, 5.6 ppm Se, 759 ppm Zn, and 86,000, 26,000, and 490 IU/kg of vitamins A, D, and E, respectively. 3 Neutral detergent fiber.

Results

Feed Intake. The total 24-hour dry matter intake (DMI) was decreased by the high fat diet (P < 0.04) but was not influenced by injections (Table 2). No interaction between diet and injection was found in total 24-hour DMI. The high fat diet decreased DMI for 2 hours after injection of vehicle (P < 0.1). A significant interaction effect of diet and injection on DMI was found for the first 2 hours after injection; MK-329 increased DMI of the high fat-fed animals by 96% over the placebo, while it decreased DMI of the low fat-fed animals by 28% compared to the placebo.

Table 2. Least squares means of amounts of dry matter eaten per given time after injection.
	Treatments1					Effects, P <
	LV	LM	HV	HM	SEM	Diet	Drug2	Diet*Drug
Postinjection, h	(kg)
-23 to 0	2.31	2.34	1.99	1.93	0.24	NS	. . .	. . .
0 to 2	1.16	0.83	0.38	0.75	0.16	0.10	NS	0.08
2 to 4	0.89	0.87	0.84	0.50	0.09	NS	NS	NS
-2 to 22	8.75	8.27	7.43	7.93	0.61	0.04	NS	NS
1 Treatments: LV = low fat + vehicle; LM = low fat + MK-329; HV = high fat + vehicle; and HM = high fat + MK-329. 2 MK-329 or vehicle. 3 Feeding was at -2 hours.

Plasma Hormones and Metabolites. The high fat diet increased plasma pancreatic concentration (Figure 1) at 2 hours postfeeding (P < 0.02). A marked reduction of plasma pancreatic polypeptide was observed in the high fat-fed animals at 1 hour after MK-329 injection, whereas no changes in plasma pancreatic polypeptide concentration were observed in response to MK-329 injection to heifers fed the low fat diet at 1 hour after injection. A significant decrease (P < 0.07) in plasma pancreatic poly-peptide occurred in all diet groups at 2 hours after MK-329 injection.

Plasma insulin concentration (Figure 2) increased gradually after feeding (P < 0.0001) but was lower in heifers fed the high fat diet before injection (P < 0.0001). There was a diet by time interaction effect on postinjection plasma insulin concentrations (P < 0.009); plasma insulin concentration continuously increased when the low fat diet was fed, whereas plasma insulin concentration did not change significantly when the high fat diet was fed. MK-329 did not influence plasma insulin concentration. Plasma glucose concentration (Figure 3) was affected by a diet by injection interaction effect at 1 hour after injection (P < 0.05); plasma glucose concentration was not altered in the low fat group but was increased by MK-329 in the high fat group.

Plasma fatty acid concentration prefeeding (Figure 4) was higher in fat-fed animals (P < 0.05); concentrations decreased rapidly after feeding (P < 0.05). Main or interaction effects of diet and injection were not observed in plasma fatty acid concentrations.

Plasma triglyceride concentration (Figure 5) was increased by feeding fat before injection (P < 0.003). MK-329 significantly decreased plasma triglyceride concentration at 2 hours after its injection (P < 0.04).

Discussion

MK-329 increased dry matter intake of the high fat diet group for the first 2-hour postinjection, while it decreased intake of the low fat group. This observation suggested that dry matter intake is regulated by different mechanisms, depending on nutrient composition of diets. The decreased intake of the low fat group with MK-329 injection was unexplained. Metabolic satiety regulators such as volatile fatty acids could have satiated the heifers fed the low fat diet. In a previous report (Choi and Palmquist, 1995), cows fed a diet high in grain had lower plasma CCK concentrations than did cows fed fat- supplemented diets. In the high fat group, lower dry matter intake after 2 hours postinjection for MK-329 might be credited to clearance of MK-329 from the body and compensatory intake when compared with that for the placebo. Plasma pancreatic polypeptide response to MK-329 supported the loss of MK-329 potency. A marked reduction of plasma pancreatic polypeptide in the high fat group at 1 hour after MK-329 injection suggested that endogenous CCK is a releasor of this hormone in dairy cattle.

Plasma insulin concentrations apparently were lowered only in the low fat group with MK-329 injection. Lowered plasma insulin concentrations in the low fat group may have been caused by lower intake by the low fat group than by the high fat group rather than due to a direct effect of MK-329. Lowered dry matter and nonstructural carbohydrate intakes usually decrease ruminal propionate production, and that l may decrease plasma insulin concentration.

MK-329 decreased plasma triglyceride concentrations at 2 hours postinjection, which might be due to lowered fat absorption from the intestine. Secretion of bile into the duodenum was presumably decreased by MK- 329, which inhibits the stimulatory effect of CCK on gallbladder contraction.

Conclusions

1. The high fat diet decreased daily dry matter in dairy cattle.

2. Inhibition of endogenous CCK activity by MK-329 attenuated fat-induced depression of dry matter intake temporarily.

3. Plasma pancreatic polypeptide concentrations were lowered by MK-329.

4. Plasma insulin concentrations were lowered by the high fat diet but not altered by the CCKA receptor antagonist.

The data support the hypothesis that endogenous CCK is a factor mediating depression of dry matter intake in dairy cattle fed the high fat diet and confirm that endogenous CCK is a secretagogue of pancreatic peptide but not of insulin secretion in dairy cattle.

Figure 1. Least square means of plasma concentrations of pancreatic polypeptide (PP) with standard errors (vertical lines) by treatments pre- and postfeeding. Treatments were low fat + vehicle (LV), low fat + MK-329 (LM), high fat + vehicle (HV), and high fat + MK-329 (HM). Feeding was at -2 hours postinjection.
Figure 2. Least square means of plasma concentrations of pancreatic polypeptide (PP) with standard errors (verticle lines) by treatments pre- and postfeeding. Treatments were low fat + vehicle (LV), low fat + MK-329 (LM), high fat + vehicle (HV), and high fat + MK-329 (HM). Feeding was at -2 hours postinjection.
Figure 3. Least square means of plasma glucose concentrations with standard errors (verticle lines) by treatments pre- and postfeeding. Treatments were low fat + vehicle (LV), low fat + MK-329 (LM), high fat + vehicle (HV), and high fat + MK-329 (HM). Feeding was at -2 hours postinjection.

Figure 4. Least square means of plasma nonesterified fatty acid (NEFA) concentrations with standard errors (verticle lines) by treatments pre- and postfeeding. Treatments were low fat + vehicle (LV), low fat + MK-329 (LM), high fat + vehicle (HV), and high fat + MK-329 (HM). Feeding was at -2 hours postinjection.

Figure 5. Least square means of plasma triglyceride concentrations with standard errors (verticle lines) by treatments pre- and postfeeding. Treatments were low fat + vehicle (LV), low fat + MK-329 (LM), high fat + vehicle (HV), and high fat + MK-329 (HM). Feeding was at -2 hours postinjection.

Acknowledgements

This research was supported in part by gifts from Merck & Co., Inc., and Purina Mills, Inc.

References

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