Drylot performance and ruminal papillae development of lambs exposed to a high concentrate diet while nursing

Smafl Ruminant Research, 7 (1992) 101-112

101

Elsevier Science Publishers B.V., Amsterdam

Drylot performance and ruminal papillae development of lambs exposed to a high concentrate diet while nursing

L. Ortega-Reyes a,l, F.D. Provenza a, C.F.

P a r k e r b a n d P.G. H a t f i e l d c °Range Science Dept., Utah State University, Logan, UT 84322-5230, USA bAnimal Science Dept., Ohio State University, Columbus, OH 43210, USA cUSDA ARS US Sheep Experiment Station, Dubois, ID 83423-9602, USA (Accepted 29 May 1991 )

ABSTRACT Ortega-Reyes, L., Provenza, ED., Parker, C.F. and Hatfield, P.G., 1992. Drylot performance and ruminal papillae development of lambs exposed to a high concentrate diet while nursing. Small Rumin. Res., 7:101-112. In 1986 (trial 1), lambs were exposed with their mothers to WB-PMP (whole barley and proteinmineral pellet ) for 15 min/d for 0, 2, 4, 8 or 16 d. In 1987 (trial 2 ), they were exposed for 0, 4 or 8 d; two treatments for 8 d, with one receiving four times more WB-PMP (8H) than the other (8L). Following exposure to WB-PMP in both years, lambs and their dams grazed on summer range for 2 months before the drylot tests. Exposure for 4 d increased (P< 0.05 ) intake of WB-PMP during the first week it was offered in dryiot in 1986, but not (P> 0.05 ) in 1987. Lambs exposed for 2, 8 or 16 d in 1986 did not consume more WB-PMP than controls (P> 0.05). In 1987, lambs in treatment 8L consumed more (P< 0.05 ) WB-PMP than controls during the first 2 weeks in drylot. Amount of WBPMP offered affected intake of WB-PMP in drylot. Lambs in treatment 8H consumed more (P< 0.05) than controls during the first 3 weeks in drylot. Lambs with high WB-PMP intakes during weeks l and 2 in both years consumed less WB-PMP during weeks 3 and 4, especially in 1987. The reduction in intake was greater for lambs previously exposed to WB-PMP than for controls. In 1986, 81% of the lambs exposed for 4 or 8 d and 64% of the lambs for 16 d achieved slaughter condition by week 8 in drylot, while only 50% and 33% of the lambs exposed for 0 or 2 d reached slaughter condition by that time (P< 0.05 ). In 1987, lambs on WB-PMP did not reach slaughter condition sooner than controls, probably due to severe decrease in intake that occurred during weeks 3 and 4 in drylot. Lambs exposed to WB-PMP for 8 d in 1987 entered the drylot with ruminal papillae that had 38% more surface area than did lambs not exposed to WB-PMP; however, the differences disappeared within 3 weeks. Results indicate that exposing lambs to a WB-PMP diet early in life enhanced performance in drylot. Development of rumen papillae as a result of exposure may contribute to this performance. LTo whom correspondence should be addressed.

0921-4488/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.

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INTRODUCTION

Livestock performance is often poor during the first 2-3 weeks in feedlots. Abrupt changes in diet, which occur when animals are placed in feedlots, can adversely affect performance for as long as 2 weeks (ToUey et al., 1988). Poor performance may occur because feed intake is low, and several days are often required before animals readily accept new feeds (Juwarini et al., 1981; Lynch et al., 1983; Mottershead et al., 1985; McDonald et al., 1988). For this reason, livestock are sometimes exposed to feeds they will encounter in the feedlot after weaning and just prior to entering the feedlot (Metre, 1970; Hillier, 1972; Taylor, 1984). The manner of exposure affects the responses of lambs to new feeds (Provenza and Balph, 1987, 1988 ). The amount ingested during exposure and after weaning is enhanced when lambs are exposed to new feeds with their mothers (Lynch et al., 1983; Thorhallsdottir et al., 1990a), and during the transition from monogastrics to ruminants (Squibb et al., 1990; Thorhallsdottir et al., 1990b; Mirza and Provenza, 1990). Rumen development during this time can be affected by type of diet. (Wardrop and Coombe, 1961; Church, 1979). Concentrate diets stimulate development of ruminal papillae more than do roughage diets (Rickard and Ternouth, 1965; Stobo et al., 1966). Thus, exposure to concentrate diets early in life may enhance responses of Iambs to such diets in feedlot. We present results of studies in which lambs were exposed with their mothers to whole barley (WB) and a protein-mineral pellet (PMP) diet for different durations. After exposure to WB-PMP, lambs foraged with their dams on rangelands prior to entering the drylot. While in the drylot, we measured intake, time to slaughter, and carcass characteristics; the development of ruminal papillae just prior to and 3 weeks after lambs entered the drylot were also measured. MATERIALS A N D M E T H O D S

Crossbred wether lambs (singles) and their dams were randomly selected each year from a flock at the USDA ARS US Sheep Experiment Station (USSES), Dubois, ID. Each year, lambs and their mothers were kept together, according to treatment, from parturition to the end of exposure. Lambs and their dams were used in two trials: trial 1 in 1986 and trial 2 in 1987. In both years, ewes and lambs were exposed to WB-PMP. The PMP consisted of a commercial sheep and lamb concentrate with 32% crude protein, 1.5 to 2.5% calcium, 1% phosphorus, and 34 000 I.U. vitamin A/kg. All ewes were offered the WB-PMP diet for 1 week prior to the time that the dams and lambs were exposed together to WB-PMP. The lambs' diet consisted of milk of their dams and alfalfa pellets (AP) ad lib. from parturition to the time of exposure

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to WB-PMP. Following exposure, lambs and their dams grazed on s u m m e r range for 2 months with a flock of ewes and lambs of about the same age. The same s u m m e r range was used in both 1986 and 1987.

Exposure In 1986, lambs averaging 6 weeks of age were randomly assigned to treatments of 0, 2, 4, 8 or 16 d of exposure to WB-PMP. Each treatment had 7 replications with 3 dams and 3 lambs per replication. Each replication was exposed as a group to 3.1 k g / d of the 80% WB-20% P M P diet for 15 m i n u t e s / d in a trough (3 m length). Each day after exposure, mothers and lambs had access to AP ad lib. from a self feeder. In 1987, lambs were exposed for 0, 4 or 8 d beginning at about 6 weeks of age. Each treatment had 10 replications with 2 dams and 2 lambs per replication. Each replication was exposed as a group to 2.1 k g / d of the 80% WB20% P M P diet for 15 m i n u t e s / d . To determine if the a m o u n t of feed offered during exposure affected intake in drylot, the 8 d treatment included two groups: one exposed to 2.1 k g / d (8L) and the other exposed to 8.3 k g / d (8H).

Intake during exposure During exposure in both years, lambs were allowed to eat with their mothers to increase learning efficiency (Thorhallsdottir et al., 1990a; Mirza and Provenza, 1990). Thus, it was not possible to measure intake of WB-PMP by individual lambs. We did, however, determine the percentage of time that individual lambs spent eating WB-PMP by recording whether or not each lamb was consuming WB-PMP at 1-minute intervals throughout the 15 minute exposure each day (Altmann, 1974). One person per treatment walked along the pens and scanned the lambs every minute. In 1987, a study was conducted to measure consumption of the WB-PMP diet by individual lambs without interference from other ewes and lambs. Fifteen lambs and their mothers were exposed separately to WB-PMP for 15 m i n u t e s / d for 8 d. A panel was placed between d a m and lamb; the panel allowed visual contact between the d a m and the lamb, but prevented them from consuming each others food.

Intake on drylot After foraging on s u m m e r range for 2 months, the lambs were weaned and transported from the USSES to Logan, UT. Drylot trials were conducted at the Green Canyon Ecology Center (GCEC) in both years. Each replicate was placed in separate pens. In 1986, lambs had ad lib. access to AP during week 1. The next week, lambs were fed 900 g A P / h e a d / d and 900 g 80% WB-20°/0 P M P / h e a d / d . From week 3 until the end of trial, lambs in each pen were offered 1.8 kg 80% WB-20% P M P / h e a d / d , but no AP. Orts were collected and weighed each

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morning before new feed was offered and intake of WB-PMP calculated by difference. In 1987, lambs were offered 1.8 kg A P / h e a d / d and 450 g 80% WB-20% P M P / h e a d / d during the first 4 d in drylot. For the next 4 d, lambs were offered the same a m o u n t of AP and 900 g 80% WB-20% P M P / h e a d / d . During the next 4 d, lambs received 1.8 kg A P / h e a d / d and 1.35 kg 80% WB-20% P M P / h e a d / d , for the remainder of the trial they were fed 1.8 kg 80% WB20% P M P / h e a d / d , but no AP.

Time to slaughter and carcass characteristics To determine whether time to slaughter varied among treatments, lamb's body condition scores (Speedy, 1980; Boggs and Merkel, 1990) were recorded at weekly intervals. Lambs were not given access to feed or water for 12 h prior to weighing. Body condition (from 1 to 10) was scored by an observer unfamiliar with the experimental design. As soon as lambs obtained a body condition score of 7, which was equivalent to 4 to 5 m m of back fat, they were weighed and removed from the trial. Every week, 2 to 3 of these lambs were selected at r a n d o m from each treatment and slaughtered. A total of ten lambs were slaughtered from each treatment at the Utah State University Meat Lab. Carcass weight, back-fat thickness and grades were recorded after carcasses had been chilled for 3 d. Rumen morphology Twenty-six lambs were randomly assigned to treatments of either 0 d ( 12 lambs) or 8 d ( 14 lambs) of exposure to WB-PMP in 1987. Management of lambs and their dams during exposure and while foraging on s u m m e r range was the same as previously described. After foraging for 2 months, 5 lambs were selected at r a n d o m from each treatment and slaughtered. The remaining lambs were placed in drylot at the GCEC for 3 weeks, and fed as previously described for lambs in 1987. After 3 weeks in drylot, these lambs were slaughtered. After slaughter, the reticulo-rumen was removed and opened by an incision from the reticulo orifice along the dorsal sac to the caudoventral blind sac. Ruminal contents were removed and each rumen was washed, drained and frozen. Prior to analysis, rumens were thawed. To measure papillae development, a 10 cm 2 section of rumen wall was selected from the atrium ruminis, both sides of the ventral sac, b o t t o m of the ventral sac, dorsal sac, caudodorsal blind sac and caudoventral blind sac. Ten papilla in each 10 cm 2 section were selected at r a n d o m and their lengths and widths measured with a millimeter rule. To measure papillae density, two 1-cm 2 samples were randomly chosen from each region of the rumen in each lamb and the number of papillae in these sections was counted. Total area of papillae was calculated by multiplying area per papilla by number of papillae per cm 2.

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Statistical analysis Results were analyzed separately for each year using least squares ANOVA for unbalanced data. The percentage of lambs from each treatment ready for slaughter each week in 1987 was analyzed by adjusting to a common back-fat thickness, using covariance analysis. Differences among treatment means were determined by the Least Significance Difference (LSD) test when the F-value was significant (P~< 0.05 ) (Montgomery, 1984). All data were analyzed using the statistical program Rummage (Bryce, 1980). RESULTS

Intake during exposure Lambs exposed for 2 d ate for only 67% of the time during exposure in 1986, whereas lambs exposed for 4, 8 or 16 d ate 81%, 89% and 85% of the time, respectively (Table 1 ). The intake of WB-PMP by lambs during exposure in 1987 varied from 7 g on d 1 to 20 g by d 8 of exposure (Table 2 ). TABLE1 Percent of a 15-min exposure period spent by lambs eating a whole barley and protein mineral pellet diet in 1986 Days of exposure at 6 weeks of age

First day

Last day

Average

2 4 8 16

54 a 77 b 72 b 68 b

79 a 84 ~b 83 ab 92 b

67 8t 89 85

a'bMeans in the same column with different superscripts differ ( P < 0.05 ); SEM = 3. TABLE 2 Intake of a whole barley and protein mineral pellet diet by individual lambs during 8 days of exposure at 6 weeks o f age in 1987 Number of days

1 2

3 4 5 6 7 8

Number of lambs

Intake (air/dry) (g/lamb/d)

15

7a

14 15 13 13 14 14 14

14b 23 c 16b 15b 14b 20 b'c 20 b'c

a,b,CMeans in the same column with different superscripts differ ( P < 0.05); SEM = 2.

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L. ORTEGA-REYESETAU

Intake on drylot During the first week in drylot in 1986, lambs exposed for 4 d ate more ( P < 0.05 ) than other lambs (Table 3 ). Intakes were similar for all treatments during week 2, and lower for the 2 and 8 d treatments than for the 0, 4, or 16 d treatments during week 3. During the first 3 weeks in drylot, average intake of lambs exposed for 0 or 4 d was similar; average intake of lambs exposed for 2, 8 or 16 d was lower ( P < 0.05 ) than for lambs exposed for 4 d. In 1987, intake varied among treatments and weeks. During week 1, lambs in treatment 8L and 8H ate more ( P < 0.05 ) than controls (Table 3). During week 2, intake increased for all treatments, and 8L and 8H again consumed more ( P < 0.05 ) than controls. The 4 d treatment was intermediate between treatments 8L and 8H and controls during the first 2 weeks in drylot. Intake for all lambs declined during week 3. Average intake of lambs in treatment 8H was greater ( P < 0 . 0 5 ) than for controls during the first 3 weeks (Table 3 ). In both years, intake of WB-PMP was similar for all treatments from week 4 until the end of the study.

Time to slaughter The majority of lambs exposed for 4 or 8 d reached slaughter condition sooner than lambs exposed for 0, 2 or 16 d in 1986 (Table 4). By week 5 in drylot, 40% of the lambs from treatments 4 and 8 d were ready for slaughter. TABLE 3

Intake (g air d r y / k g B W / d ) of a whole barley and protein mineral pellet (WB-PMP) diet by lambs in drylot in 1986 and 1987 Days of exposure at 6 weeks of age

Weeks in Drylot 1

0 2 4

14 a 14• 19 b

8 16 SEM

13 ~ 15 a 1.2

0 4 8L 8H SEM

14" 15 "b 18 b

17 b 1.1

Average 2 1986 32 a 26 ~ 32" 28 a 28 a 1.8 1987 24" 26 a,b 29 b'c 35 1.4

25 a,b 22 ~ 27 b

24 a,b 21 ~ 26 b

22 ~ 25 ~'b 1.3

21 • 23" 0.95

17 b 16 b 11 a 19 b 1.8

18 a 19 ~,b 19 a,b 22 b 0.94

' L a m b s were exposed to different amounts of WB-PMP in 1987; lambs in 8H were given four times more WB-PMP/d during exposure than lambs in the 4 d a n d 8L d treatment. a'b'cwithin years, means in the same column with different superscripts differ ( P < 0.05).

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107

TABLE 4 C u m m u l a t i v e percentage o f l a m b s ready for slaughter in 1986 and 1987 Days o f exposure at 6 weeks o f age

Weeks in drylot 1986 5

8

11

0 2 4 8 16

24 a'b 14 a 40 b 40 b 16 a

50 a'b 33 ~ 81 c 81 c 64 b,c

95 a 90 a 95 ~ 90 a 88 ~

Days o f exposure at 6 weeks o f age

Weeks in drylot 1987 7

10

15

0 4 8L 8H

0a 0a 23 b 21 b

53 a 48 a 48 a 66 a

83 a 98 a 93 a 81 a

a'b'cWithin years, m e a n s in the same c o l u m n with different superscripts differ ( P < 0.05). SEM for 1986 = 8; SEM greater than zero for 1987 = 7.

By week 8, 81% of the lambs from treatments 4 and 8 d had reached slaughter condition, compared to 3 3 0 , 5 0 % and 64% of the lambs from the 2, 0 and 16 d treatments, respectively. By week 11, most lambs had reached slaughter condition and we ended the trial. In 1987, 2 3 0 and 21% of lambs in treatments 8L and 8H were ready for slaughter by week 7 in drylot. None of the 0 or 4 treatment were ready for slaughter by week 7 (Table 4). From week 10 until the end of the trial, there were no differences among treatments.

Body and carcass characteristics In 1986, there were no differences ( P > 0.05 ) in the initial body condition, carcass weight, back-fat thickness, or grade among treatments (Table 5). Control lambs weighed less ( P < 0.05) at the start of the drylot phase than lambs exposed for 8 or 16 d. Lambs from treatments 8 and 16 weighed more ( P < 0 . 0 5 ) at the end of the drylot trial than controls (Table 5). In 1987, carcasses of lambs from treatment 8L were heavier ( P < 0.05 ) than those from lambs in treatments 0 and 4 d (Table 5). Lambs in 8L also had more backfat than controls at P < 0.10. In both years, lambs in all treatments graded choice. Rumen morphology Ruminal papillae of lambs exposed to WB-PMP had 38% more surface area than controls after foraging on summer range from June to August (Table 6 ). Their ruminal papillae were longer ( P < 0 . 0 5 ) ; there was no treatment×rumen-site interaction ( P > 0 . 0 5 ) . Lambs in both treatments had longer papillae in the atrium ruminis, and shorter papillae in the bottom of the ventral sac. There was virtually no papillae development in the bottom of the ventral sac of controls. Density of papillae was similar for all lambs. Papillae were most dense in the caudodorsal blind sac, caudoventral blind sac

L. ORTEGA-REYES ET AL

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TABLE 5 Effects o f duration o f exposure to a whole barley and protein mineral pellet diet on body and carcass characteristics o f lambs in drylot in 1986 and 1987 Days o f exposure

year

IBC t

FBC t

IBW t (kg)

FBW ~ (kg)

CW ~ (kg)

BFTI (mm)

G~

0 2 4 8 16 SEM 0 4 8L 8H SEM

1986

4.4 a 5.(P 5.1`5.1 ~ 5.3`0.2 5.2`5.4" 5.1 a 5.4`0.2

7.(P 7.2 a'b 7.2 a,b 7.5 c 7.3 b,~ 0.07 6.9`7.0 a 6.9`6.9`0.6

34 a 37 `-'b 37 `-,b 39 b 38 b 1 34 a 34`33 ~ 34 a 1

45 a 45`46 a'b 49 c 48 b'c 1 46`47 ~ 49" 47`1

20 a 21`21`22`2P 0.9 20" 2P 23 b 22 a,b 0.8

4.9 a 5.1`5.6 a 5.5 a 4.9 a 0.5 4.4 ~ 4.9 ~'b 6.0 b 4.8 `-'b 0.5

C C C C C

1987

C C C C

q B C = i n i t i a l body condition; F B C = f i n a l body condition; I B W = i n i t i a l body weight; F B W = f i n a l body weight; C W = carcass weight; BFT = back fat thickness; G = grade (C is choice ). a'b'cWithin years, m e a n s in the same column with different superscripts differ ( P < 0.05); back fat thickness in 1987 ( P < 0 . 1 0 ) .

TABLE 6 R u m i n a l papillae d e v e l o p m e n t in lambs exposed to a whole barley and protein-mineral pellet diet at 6 weeks o f age Treatment

Length (mm)

Width (mm)

Area per papilla ( m m 2)

Density (per c m 2)

Total area o f papillae (ram 2 per c m 2 )

1.6`1.4 b 0.08

7.8 a 5.6 b 0.6

58 ~ 59`2.2

460`338 b 43

1.5 a 1.4`-

7.5 a 6.4`-

54 ~ 67`-

410 a 448 a

After 2 months on summer range Exposed N o t exposed SEM

2.5`1.9 b 0.2

After 3 weeks in drylot Exposed Not exposed

2.4 a 2.3 a

a'bWithin periods, m e a n s in the same column with different superscripts differ ( P < 0.05 ); width after 2 m o n t h s on s u m m e r range ( P < O. 10 ). SEM after 3 weeks in drylot: length 0.1; width 0.05 (exposed) and 0.06 (not exposed); area/papilla 0.05 ( e x p o s e d ) 0.06 ( n o t exposed); density 4.5 ( e x p o s e d ) and 5.3 (not exposed); total area 24 ( e x p o s e d ) a n d 28 ( n o t exposed).

and atrium ruminis, and less dense on the left side of the dorsal sac and the bottom of the ventral sac. After 3 weeks in drylot, there were no differences in the papillae of treatment and control lambs (Table 6).

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DISCUSSION

The amount of WB-PMP ingested during exposure at 6 weeks of age affected the amount of WB-PMP ingested in drylot 2 months later. Lambs in 8H ingested more WB-PMP than controls during the first 3 weeks in drylot in 1987. We did not, however, find a consistent relationship between duration of exposure and intake. For instance, lambs exposed for 4 days in 1986 ingested more WB-PMP in drylot than lambs exposed for 2, 8 or 16 d, while lambs exposed for 4 days in 1987 were intermediate between controls and lambs exposed for 8 days (8L or 8H). Likewise, lambs exposed for 8 days in 1986 did not ingest more WB-PMP than controls, while lambs exposed for 8 days (8L) in 1987 ingested more WB-PMP than controls during the first two weeks in drylot. These inconsistencies may have been caused by the method we used to expose lambs to WB-PMP. Lambs were allowed to eat with their mothers during exposure to WB-PMP in an attempt to increase learning efficiency (Thorhallsdottir et al., 1990a,b; Mirza and Provenza, 1990), and to simulate management conditions used by some ranchers. However, ewes quickly consumed the majority of the WBPMP during the 15-minute exposure, and as a result, their lambs ingested little WB-PMP during exposure. The maximum amount that a lamb could have consumed was less than 1 to 2% (7 to 23 grams, Table 2) of WB-PMP offered daily to each ewe-lamb group ( 1000 g). The high intake of WB-PMP by lambs in 8H during the first 3 weeks on drylot strongly suggests that lambs in treatments 2, 4, 8L and 16 were unable to ingest enough WB-PMP during exposure in 1986 and 1987 to affect intake of WB-PMP in drylot. Merely being exposed for longer durations did not ensure that lambs would ingest more WB-PMP, because lambs were competing with their mothers daily for a limited amount of feed. Thorhallsdottir et al. (1990a) found that lambs' intake of a novel food did not increase after weaning if lambs were only able to observe their mothers ingest the food prior to weaning. Intake decreased during week 3 in drylot, and the decrease was greater in 1987 (42%) than in 1986 ( 17% ); moreover, the decrease was greater for lambs exposed to WB-PMP early in life (4d=36%; 8L=59%; 8H=37%) than for controls (25%) in 1987. The decrease in intake was associated with a decrease in body weight and condition. Three weeks passed before lambs regained their initial body weight, and 4 weeks passed before they regained their initial body condition. Over-ingestion of WB-PMP during the first two weeks in drylot, combined with a lack of roughage in the diet, caused acidosis which caused the decrease in intake. When ruminants overingest rapidly fermentable concentrate feeds, they develop acidosis. Acidosis is caused by an accumulation of lactic acid and other organic acids in the rumen and other tissues (Elam, 1970), and the symptoms include reduced ruminal pH, damage to ruminal epithelium, and a decrease

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L. ORTEGA-REYES ET AL.

in feed intake (Lee et al., 1982). Maintaining a sizable amount of roughage in the diet (25% to 40%) prevents acidosis, and resultant decline in intake and performance during the early stages of adaptation to high energy diets (Grovum, 1988 ). Sheep fed high energy diets consume less digestible energy than on low ( < 60%) energy diets (Grovum, 1988 ). Eighty-one percent of the lambs exposed to WB-PMP for 4 d in 1986 were ready for slaughter after 8 weeks in the drylot (Table 4); this result is consistent with their generally higher intake of barley during the first 3 weeks in drylot (Table 3 ). However, lambs exposed for 8 d in 1986 finished as soon as those exposed for 4 d (Table 4), even though they generally consumed less feed during the first 3 weeks in drylot (Table 3 ). These apparently inconsistent results may be explained in part by the enhanced development of rumen papillae (Table 6). The ruminal papillae of lambs exposed to WB-PMP for 15 min/d for 8 d had 38% more surface area than lambs not exposed to WB-PMP, even after 2 months of foraging on summer range (Table 6). Better papillae development may have helped lambs absorb more volatile fatty acids and ammonia released during the microbial fermentation of WB-PMP (Rickard and Ternouth, 1965; Sengar and Singh, 1970; Church, 1979 ), and thus enhanced body growth. Conversely, exposing lambs to WB-PMP in 1987 did not improve performance relative to controls (Table 4), probably due to decline in intake of treatments 4, 8L and 8H during weeks 3 and 4 in drylot. Development of ruminal papillae depends in part on chemical stimulation, particularly from volatile fatty acids and ammonia released from microbial fermentation of feed. Increases in butyric and propionic acids are positively correlated with papillary development while increases in acetic acid are inversely related (Omar et al., 1964). Propionic and butyric acids increase and acetic acid declines when high energy diets are fed (Harrison et al., 1960; Stobo et al., 1966; Lee et al., 1982 ). The chemical characteristics of the forage that lambs ingested on summer range may have further stimulated the development of ruminal papillae, given that papillae size is positively correlated with the nutritional quality of the forage (Langer, 1984, 1988; Hofmann and Schwartz, 1987; Hofmann, 1988). IMPLICATIONS

Our results suggest that lambs exposed to WB-PMP early in life with their mothers will ingest more WB-PMP during the first 3 weeks in drylot than lambs naive to WB-PMP. However, lambs exposed to WB-PMP may overingest WB-PMP to their detriment in the drylot, if the amounts of WB-PMP and roughage are not carefully regulated. Moreover, our findings suggest that if intake is carefully controlled during the first 3 weeks in drylot, lambs familiar with WB-PMP may reach finish body condition sooner than lambs naive to

DRYLOTPERFORMANCEOFLAMBS

111

WB-PMP. We suggest that this response is due to the enhanced intake of WBPMP, and that it may also be due in part to enhanced development and function of rumen papillae as a result of exposure to WB-PMP early in life. More research is needed to clarify the relationship between amount of exposure to WB-PMP early in life and lamb performance in drylot. In addition, research is needed to determine the conditions under which rumen papillae will remain larger in lambs exposed to WB-PMP after foraging on summer range; the results may depend on the nutritional quality of the forage, which can vary from year to year depending on amount of precipitation. ACKNOWLEDGEMENTS

Financial support for the senior author was provided by the Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP-SARH) from Mexico and Cooperative State Research Service (CSRS). We gratefully acknowledge Onelia Lizarraga de Ortega for help in data collection and the USDA ARS US Sheep Experiment Station for material support. Published with the approval of the Director, Utah Agricultural Experiment Station, Utah State University, Logan, UT as Journal Paper No. 3747.

REFERENCES Altmann, J., 1974. Observational study of behavior: Sampling methods. Behavior, 49: 225-267. Boggs, D.L. and Merkel, R.A., 1990. Live Animal Carcass Evaluation and Selection Manual. Kendall/Hunt Publishing Co., Dubuque, IA, 221 pp. Bryce, G.R., 1980. Data analysis on Rummage. A user's guide. Brigham Young Univ. Dept. of Statistics, Provo, UT, 172 pp. Church, D.C., 1979. Growth and development of the ruminant stomach. In: D.C. Church (Editor), Digestive Physiology and Nutrition of Ruminants. Volume l, Digestive Physiology. O & B Books, Corvallis, OR, pp. 34-45. Elam, C.J., 1970. Starting cattle on feedlot rations. Feedlot, 12: 18-20. Grovum, W.L., 1988. Appetite, palatability and control of feed intake. In: D.C. Church (Editor), The Ruminant Animal. Prentice Hall, Englewood Cliffs, N J, pp. 202-216. Harrison, H.N., Warner, R.G., Sander, E.G. and Loosli, J.K., 1960. Changes in the tissue and volume of the stomachs of calves following the removal of the dry feed or consumption of inert bulk. J. Dairy Sci., 43: 1301-1312. Hillier, R.J., 1972. Preconditioned calves are remunerating ruminants. Feedlot, 14:10-1 I. Hofmann, R.R., 1988. Anatomy of the gastrointestinal tract. In: D.C. Church (Editor), The Ruminant Animal. Prentice Hall, Englewood Cliffs, NJ, pp. 14-43. Hofmann, R.R. and Schwartz, H.J., 1987. Morphological adaptation of the forestomach of small east African goats to seasonal changes of forage quality. In: Proc. IV Internl. Conf. on Goats, Brazilia, Brazil, EMBRAPA, march 8-13, pp. 1440-1441. Langer, P., 1984. Comparative anatomy of the stomach in mammalian herbivores. Quart. J. Exp. Physiol., 69:615-625. Langer, P., 1988. The Mammalian Herbivore Stomach: Comparative Anatomy, Function and Evolution. Gustav Fischer Verlag, New York, 557 pp.

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