Effects of photoperiod and feeding whole maize, whole barley, or rolled barley on growth performance and diet digestibility in veal calves

LivestockProductionScience 44 ( 1995) 27-36

Effects of photoperiod and feeding whole maize, whole barley, or rolled barley on growth performance and diet digestibility in veal calves G. GuertinaYb,B. Lachancea, G. Pelletier”, G.J. St-Laurentb, G.L. Roy”, D. Petitclercav* aAgriculture and Agri-Food Canada, Lennoxville, Quibec, Canada, JIM 123 bDPpartement des sciences animales, Universite Laval, Qudbec, Q&bee, Canada, GI K 7P4

Accepted20 June 1995

Abstract

Fifty-seven black and white male dairy calves, reared from 48 to 222 kg liveweight, were used to study the effects of photoperiod and feeding whole maize (75%; WM), whole barley (80%; WB) or rolled barley (80%; RB) based diet after weaning. Photoperiod treatments were 10 h of light (L):14 h of dark (D), 16L:8D, IOL: 14D for 6 weeks then followed by 16L:8D, or 16L:8D for 6 weeks then followed by lOL:14D. During weeks 17 and 20, 30 calves of uniform weight, ten per feeding treatment, underwent two digestibility trials. Exposure to 16L:8D photoperiod or a change from 16L:8D to 1OL:14D increased similarly weight gain by 6.6% and feed intake by 9.5% without affecting feed efficiency. Calves fed WM consumed less feed (P < 0.05), had similar average daily gain (ADG) and were 25% more efficient than calves fed WB but calves fed RB had a lower average daily feed intake (P < O.OS), had similar ADG and were 10% more efficient than WB-fed calves. Calves fed RB had a tendency to have higher (P=O.O7) carcass weight and dressing percentage ( 118.8 kg and 53.6%, respectively) than calves fed WB ( 115.4 kg and 52.0%, respectively). Body and meat composition, meat color, and haematocrit and haemoglobin levels were not significantly affected by feeding or photoperiod treatments. Digestibility of dry matter (DM) , energy (E), nitrogen, starch (S), phosphorus (P) and copper (Cu) were higher (P
* Corresponding

author.

Elsevier Science B.V. SSD10301-6226(95)00052-6

Cereal; Rolling barley

28

G. Guertin et al. /Livestock

Production Science 44 (1995) 27-36

1. Introduction

Photoperiod will affect growth and development of ruminants (Petitclerc and Zinn, 1991). In cattle, longday photoperiod can increase body growth and feed intake, and improve feed efficiency of dairy heifers (Peters et al., 1978,198O; Petitclerc et al., 1983). However, Roche and Boland ( 1980) and Sorenson ( 1983) did not observe any significant effect of photoperiod in very young calves. Furthermore, Zinn et al. (1986) reported no significant effects on weight gain and feed intake of prepubertal heifers exposed to 8 or 16 h of light per day as opposed to post-pubertal heifers. These contradictory results could be explained by the animal’s previous photoperiod exposure which might affect response to a subsequent photoperiod signal (Zinn et al., 1988). Today, there is no information available on the effects of photoperiod on the digestibility of nutrients. Prolactin, the hormone most affected by a change in photoperiod (Tucker and Ringer, 1982)) could increase, as suggested by Eisemann et al. ( 1984), the absorptive capacity of the intestines and thus increase nutrient absorption. Rearing calf on a concentrate diet after weaning is an alternative to traditional milk-fed veal production system. Dietary iron levels are relatively higher when calves are fed a grain based diet. Hence, subclinical anemia should not be a problem. However, these calves will give a darker meat product (Beauchemin et al., 1990). In general, maize or barley are the main ingredient in the diet of grain-fed calves. However, it has been demonstrated that steers and calves were less efficient in utilizing a diet based on whole barley than a diet based on whole maize (Kay et al., 1972; Latrille et al., 1983; Beauchemin et al., 1990). Several studies (Gardner and Wallentine, 1972; Kincaid, 1980; Murdock and Wallenius, 1980; Hironaka et al., 1992) have demonstrated that rolled barley can be used as the only grain in the diet of veal calves. Indeed, grinding or breaking the seed coat will improve the availability of nutrients for digestion (Deyoe, 1976; Hironaka et al., 1992) and the palatability of the grain (Hale, 1973) resulting in a more efficient weight gain (Deyoe, 1976; Hironaka et al., 1992). However, none of these studies have directly compared maize and barley as well as the physical treatment of barley on calf performance and diet digestibility.

Therefore, our objectives were to examine the effects of photoperiod and to compare the type of cereals (whole maize vs. whole barley) and the effects of rolling barley on growth performance, carcass composition and diet digestibility, on energy and nitrogen retentions, and on blood urea level in grain-fed veal calves.

2. Material and methods Sixty black and white male dairy calves were purchased at a local auction at about 1 week of age. They were randomly distributed between two heated and photoperiod controlled rooms. The animals were exposed to either 10 h of light (L) : 14 h of dark (D) or 16L:8D using fluorescent lights (200 lx at eye level). Room temperature was kept at 20°C and calves were housed in individual elevated cages. Blood samples were taken two days after their arrival for haemoglobin and haematocrit tests. Calves with haematocrit results under 40 were injected with iron-dextran ( 100 mg per unit below 40 with a maximum of 500 mg/day and 1000 mg/calf). Calves were fed a commercial milk replacer twice a day until weaning. A commercial starter diet was provided ad libitum after the fourth day. Calves were given free access to automatic waterers after day 10 and were weaned when they consumed between 500 and 600 g of starter per day for three consecutive days and had gained at least 10 kg of body weight. During this period, two animals were eliminated for health reasons. During the 6th week after arrival, half the animals exposed to lOL:14D or 16L:8D were randomly redistributed and exposed respectively to 16L:8D or lOL:14D for 15 additional weeks (week 7 to 21); the other half remained under the same photoperiod. Then, all calves within each photoperiod group, were randomly assigned to one of three fattening diets: one maize diet made up of whole maize (WM) and a protein-mineral-vitamin supplement with cane molasses and two barley diets made up of whole (WB) or rolled (RB) barley and a protein-mineral-vitaminsupplement with cane molasses. During this period, one animal was eliminated for health reasons (i.e., bloating). The chemical composition of each diet is given in Table 1. All calves were fed individually ad libitum between weeks 7 and 21. Weights of feed offered and refused were individually recorded every day. Diets were sam-

G. Guertin et al. /Livestock Table 1 Composition

Production Science 44 (1995) 27-36

of the diets

Ingredient?

Die? WM

Whole maize Whole barley Rolled barley Soybean meal, 48.5% CP Rapeseed meal (canola)(38% CP Meat and bone meal, 45% CP Alfalfa meal, 17% CP Limestone 0.33 salt Dynamate (KC 1) ,50% K Lignin sulfonate Trace minerals and vitamins premix Cane molasses Nutrient content“ Dry matter (%) Energy (Kcal/g) Nitrogen (%) Starch (%)’ ADF (%o) Calcium

29

(o/o)

Phosphorus

(%)

Iron (ppm) Copper ( wm)

WB

RB

72.50 77.50 _ 8.45 6.25 3.75 5.00 0.40 0.40 0.20 0.22 0.15 2.75 88.40 4.70 3.20 (3.20)’ 29.90 8.80 (8.80) 1.08 (1.11) 0.77 (0.78) 218.00 48.00

5.23 4.44 3.75 5.00 0.40 0.40 0.16 0.22 0.15 2.75 88.40 4.50 3.40 (3.50) 21.40 16.20 (16.00) 1.45 (1.51) 0.75 (0.77) 248.50 45.50

77.50 5.23 4.44 3.75 5.00 0.40 0.16 0.22 0.15 2.75 88.10 4.60 3.30 (3.20) 24.50 15.60 (14.20) 1.34 ( 1.23) 0.73 (0.71) 242.00 57.50

“On a dry matter basis. “WM. whole maize diet; WB, whole barley diet; RB, rolled barley diet. ‘From samples taken during digestibility trial. “‘From weekly samples taken between weeks 7 and 21.

pled weekly and cornposited in 3-week periods. Samples were analyzed for dry matter (AOAC, 1980), nitrogen and phosphorus (digestion according to AOAC, 1980, followed by calorimetric determination according to Reardon et al., 1966; Crooke and Simpson, 1971), acid detergent fiber (Goering and Van Soest, 1970) and calcium (digestion according to AOAC, 1980 and determination by atomic absorption using a Varian Tecktron, model 1250). Calves were weighed every 3 weeks and slaughtered at an average liveweight of 222 kg. Animals were slaughtered in groups of 12 (one animal per treatment combination), twice a week, over a 3 week period, starting after week 21. Prior to shipment, body weight, heart girth and withers height were recorded. A blood sample was taken to determine

haemoglobin and haematocrit levels. At the slaughterhouse, chilled carcass weight and meat color were determined and carcasses were classified by a grader of Agriculture and Agri-Food Canada based on visual appraisal of meat color (Anonymous, 1984). Thymus glands were collected and weighed. The 9-10-l 1th rib section was cut, deboned, and ground (Hankins and Howe, 1946) before analysis of dry matter, protein (AOAC, 1980) and fat (Folch et al., 1957) contents in order to estimate carcass composition. The rib eye section of the 12th rib was also taken to determine meat dry matter, protein (AOAC, 1980) and fat (Folch et al., 1957). During week 17, 30 calves of uniform weight, ten per feeding treatment, were used for a first digestibility

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G. Guertin et al. /Livestock Production Science 44 (1995) 27-36

trial with total fecal collection. The same calves were used again during week 20 for a second digestibility trial with total fecal and urinary collections. Feed samples were taken every day and composited by week. Feces were collected daily. 10% of the total feces weight was sampled and frozen every day for seven consecutive days. Then, feces were thawed, mixed, and a pooled sample was taken for chemical analysis. Each day, 5% of the total urine weight was sampled and always frozen in the same container. Then, urine was thawed and a sample was taken for chemical analysis. Feed and feces were analyzed for dry matter ( AOAC, 1980)) t&ogen and phosphorus (digestion according to AOAC, 1980 followed by analysis according to Reardon et al., 1966; Crooke and Simpson, 197 1)) acid detergent fibre (Goering and Van Soest, 1970) and calcium (digestion according to AOAC, 1980 and analysis by atomic absorption using a Varian Techtron, model 1250). Other analysis included iron and copper (Isaac and Kerber, 197 1) and energy (ballistic bomb calorimeter made by Gallenkamp) . Starch was determined enzymatically by the method of Thivend et al. ( 1972). Free glucose was determined by the GODPAP method (kit from Boehringer Mannheim Canada, 1979). Urine samples were analyzed for dry matter, nitrogen ( AOAC, 1980)) and energy (bomb calorimeter). Before sending calves to the slaughterhouse, a blood sample was taken to determine blood urea level (kit from Boehringer Mannheim Canada, 1979). Analyses of variance were carried out as a 2 X 2 X 3 factorial arrangement design (Gill, 1978) to study the effects of photoperiod treatments (main effects of 8L:16D or 16L:8D photoperiod before and after week 6) and diets (WM vs. WB vs. RB) on feed consumption, weight gain, feed efficiency, on nutrient digestibility, on energy and nitrogen retentions, and on blood urea level. Data for repeated measurements were analysed as a split plot in time according to Gill ( 1978). Analysis of covariance were carried out on carcass traits using body weight at slaughter as covariate (Steel and Torrie, 1980). The analysis for energy and nitrogen retentions used values of the second digestibility trial only. Linear contrasts were used to evaluate the differences between photoperiod treatments and Scheff&‘s test was used to evaluate differences due to diets. The interaction between photoperiod treatments and diets was evaluated but should be interpreted with caution due to the limited number of animals per cell.

3. Results During the experimental period, weight of calves maintained under 1OL:14D (group 1) , switched from 1OL:14D to 16L:8D (group 2), switched from 16L:8D to lOL:14D (group 3) or maintained under 16L:8D (group 4) increased from 66.9 to 189.8 kg, 65.8 to 183.4 kg, 67.1 to 195.2 and 68.4 kg to 196.8 kg, respectively (Fig. 1). There was no significant effect (P> 0.05) of photoperiod on overall average body weight but there was a significant photoperiod by time interaction (P = 0.02). Average daily gain between weeks 7 and 21 of animals exposed to 16L:8D during weeks 1 to 6 (groups 3 and 4) was greater than ADG of animals exposed to 1OL:14D during the same period (groups 1 and 2; Fig. 1 and Table 2). Similarly, average daily dry matter intake (DDMI) was greater (P < 0.01) for animals exposed to 16L:8D during weeks 1 to 6 as compared to calves exposed to 1OL:14D (Table 2). There was no significant effect (P > 0.05) on overall feed/gain ratio. On the other hand, growth rate, DDMI and feed/gain ratio were not affected by subsequent photoperiod treatments ( lOL:14D vs. 16L:8D between weeks 7 to 21). In addition, there was no interaction effect due to switching photoperiod from 1OL:14D to 16L:8D or vice versa as compared to continuous photoperiod exposure (Fig. 1 and Table 2). During the period between weeks 7 to 2 1, calves fed WM, WB, or RB increased in liveweight from 67.5 to 193.6 kg, 67.0 to 189.6 kg, and 66.7 to 190.7 kg, respec200

4

;

180

~lOL14DtolOL:14D c/

lOL.14D to 16L:BD

+

2160

5 140 ! .i P120 4

&lD tol%bBD

(IJ

& $loo

T

+

16L BD to lOL’14D t 9

; :

80 :

/,/

,’

Fig. 1. Growth rate of calves exposed to continuous lOL:14D, lOL:14D followed by 16L:8D, 16L:8D followed by lOL:14D or continuous 16L18D.

C. Guertin et al. /Livestock Production Science 44 (1995) 27-36

31

Table 2 Daily dry matter intake ( DDMI) , average daily gain ( ADG) , and feed/gain Parameter

of calves exposed to different photoperiods”

Photoperiod l-6 wk 7-21 wk

DDMI (kg/day) ADG (kg/day) Feed/gain (DDMUADG)

Contrast

lOL:14D lOL:14D

1OL: 14D 16L:8D

16L:8D lOL:14D

16L:8D 16L:8D

1+2

1+3

1+4

VS.

vs.

vs.

(1)

(2)

(3)

(4)

3+4

2+4

2+3

3.58rtO.12 1.17*0.03 3.06rtO.08

3.55f0.13 1.12+cO.O3 3.16rtO.08

3.93*0.13 1.22 * 0.03 3.22 f 0.08

3.88f0.12 1.22*0.03 3.20 f 0.08

** * NS

NS NS NS

NS NS NS

“Values are least square means f standard error of means. *p
tively. There were no significant effects (P > 0.05) of diets or diet-by-time interaction on body weight changes. Overall, average daily gain was 1.19 kg/day (Table 3). Dry matter intake was higher (P< 0.05) for calves fed WB (4.08 kg/day) than for those fed WM (3.37 kg/day) or RB (3.74 kg/day) (Table 3). Therefore, calves on WB were less efficient (P< 0.05) in converting feed into weight gain than calves fed WM and RB (3.50 vs. 2.80 and 3.18 kg DDMI/kg gain). On the other hand, DDMI was lower (P< 0.05) and feed/gain improved (P< 0.05) in calves fed RB as compared with WB. Slaughter weight was less (P< 0.05) in animals fed WB (220.1 kg) as compared to those fed WM (223.5 kg) and RB (222.7 kg). In addition, chilled carcass weight without the skin was less (P< 0.05) in calves fed WB ( 115.4 kg) than those fed RB ( 118.8 kg).

However, there were no significant effects (P> 0.05) of diet on days in barn ( 173.8 days), dressed yield (53.0%), heart girth ( 137.5 cm), withers height ( 107.3 cm), thymus weight (485.1 cm), and carcass grade. There were no significant effects of photoperiod or photoperiod-by-diet interaction on any of these measurements. In addition, there were no significant effects of diet, photoperiod, or diet-by-photoperiod interaction on haemoglobin and haematocrit levels, meat color, and meat and body composition. Digestibility of dry matter, energy, nitrogen, starch, phosphorus, and copper were significantly higher (P< 0.05) for calves fed WM diet than for calves fed WB (Table 4). Digestibility of dry matter, energy, starch, phosphorus, and copper was less (P< 0.05) for the diet containing WB (69.2, 67.7, 69.0, 54.9 and 32.8%) than the diet containing RB (74.3, 73.1, 84.1,

Table 3 Daily dry matter intake (DDMI), baarley (RB)a Parameter

n DDMI (kg/day) ADG (kg/day) Feed/gain

average daily gain (ADG)

and feed/gain

of calves fed whole maize (WM),

Diet

Contrast

WM (1)

WB (2)

RB (3)

18 3.37f0.11 1.20 f 0.03 2.80 f 0.07

20 4.08rtO.10 1.17*0.02 3.50 * 0.06

19 3.74f0.12 1.18f0.03 3.18f0.08

(DDMl/ADG) ?‘alues are least square means f standard error of means. *p
whole barley (WB), or rolled

1 vs. 2

2 vs. 3

*

*

NS *

NS *

G. Guertin et al. /Livestock Production Science 44 (1995) 27-36

32

Table 4 Nutrient digestibilities ( 0) of whole maize (WC), whole barley (WB) and rolled barley (RB) based diets” Nutrient

Dry matter Energy Nitrogen Starchb ADF Calcium Phosphorus Iron Copper

Feeding treatment

Contrast

WC

WB

RB

80.7 f 1.30 80.0f 1.39 79.2 f 1.24 88.6 f 1.86 63.0 f 1.24 73.0* 1.20 73.8 f 2.89 56.3f 1.81 55.7 f3.44

69.2 f 1.06 67.7f 1.14 73.4 f 1.02 69.0 f 1.52 65.7 f 1.02 73.3 f 0.98 54.9 f 2.34 53.0&-1.48 32.8f2.81

74.3 f 1.06 73.1 f 1.14 76.7 f 1.02 84.1 f 1.52 62.1k1.02 74.7 f 0.98 64.4 f 2.34 54.6* 1.48 44.0k2.81

WC vs. WB

WB vs. RB

* * NS * NS NS

NS NS *

NS

NS *

* *

“Values are least square means f standard error of means. bGlucose free starch. *p
64.4, and 44.0%); there was no difference in nitrogen digestibility between both barley diets. Digestibility of calcium and iron was not significantly different among diets. The digestibility of fibre (ADF) was different between the two digestibility trials; overall, fibre digestibility was higher during the first trial than during the second. However, ADF digestibility was not affected by diets. Photoperiod treatments did not affect digestibility of nutrients. Diets did not influence energy intake (Table 5). However, calves fed WM tended (P = 0.06) to have a lower energy intake per kg BWe75 ( 1.48 MJ/day) than calves fed WB ( 1.78 MJ/day) and RB ( 1.85 MJ/day) . Fecal and urinary energy were higher for calves fed WB than for calves fed WM. Therefore, total energy excreted per kg BWe.75for calves fed WB (0.62 MJ/ day) was significantly higher (P < 0.05) than for those fed WM (0.34 MJ/day ). Energy retained was not significantly different among diets but, when expressed as a percentage of energy intake, was higher (P < 0.05) with WM (77.2%) than with WB (64.7%). Energy intake, total energy excreted, and energy retained were not significantly different between rolled and whole barley diets. However, when energy retained was expressed as a percentage of energy intake, calves fed RB (69.8%) retained more energy (P <0.05) than those fed WB (64.7%). Photoperiod treatments did not affect energy intake, energy excreted, and energy retained.

Types of grain in the diet affected nitrogen intake (Table 6). Calves fed WM had a lower (P <0.05) nitrogen intake per kg Bw7’ (2.28 g/day) than those fed WB (3.04 g/day). Fecal, urinary, and total nitrogen excreted were significantly lower (P < 0.05) for WM than for WB. However, nitrogen retained or nitrogen retained expressed as a percentage of nitrogen intake were not different among diets. Nitrogen intake, excreted, and retained were not significantly different between the two barley diets. Photoperiod treatments did not influence nitrogen intake, excreted and retained. Calves fed WM had less (P <0.05) urea in their blood (17.7 mg/lOO ml) than calves fed WB (24.9 mg/ 100 ml). There was no significant difference for blood urea levels between whole and rolled barley (26.1 mg/ 100 ml) diets. Photoperiod treatments did not affect blood urea levels. There were no significant interaction between photoperiod and diet treatments for any of the variables measured except on body weight changes (P < 0.01) . This interaction was the result of a slower growth rate of animals fed RB and switched from lOL:14D to 16L:8D. In addition, weight gain was less in animals fed WB and subjected continuously to 16L:8D.

4. Discussion These results clearly show that initial photoperiod exposure might affect the animal’s responsiveness to a

G. Guertin et al. /Livestock Production Science 44 (1995) 27-36

33

Table 5

Energy partitioning of calves fed whole maize (WC), whole barley ( WB) , or rolled barley ( WEJ) based diets’ Energyb (MJ/day)

Energy intake Fecal energy Urinary energy Total energy excreted Energy excreted’ Digestible energy intake Energy retained Energy retained’

Feeding treatment

Contrast

WC

WB

RB

WC vs. WB

WB vs. RB

1.48*0.11 0.29 +0.04 0.05 f 0.002 0.34 f 0.04 22.8 f 1.45 1.19f0.08 1.14rtO.08 77.2 It 1.45

1.78 f 0.09 0.57 f 0.03 0.06 f 0.002 0.62 f 0.03 35.3 f 1.16 1.21 f0.07 1.15+0.07 64.7kl.16

1.s5*0.09 0.50 f0.03 0.06 f 0.002 0.56 f 0.03 30.2i 1.16 1.35 f 0.07 1.29 f 0.07 69.8* 1.16

NS * * * *

NS NS NS NS *

NS NS *

NS NS *

‘Values arc least square means + standard error of means. “Per kg of metabolic body weight. ‘Expressed as a percent of the energy intake. *p
Table 6 Nitrogen retention of calves fed whole maize (WC), whole barley (WB), or rolled barley (RB) diets” Nitrogen” (g/day)

Nitrogen intake Fecal nitrogen Urinary nitrogen Total nitrogen excreted Nitrogen excretedC Digestible nitrogen Nitrogen retained Nitrogen retained’

Feeding treatment

Contrast

WC

WB

RB

WC vs. WB

WB vs. RB

2.28kO.19 0.47 f 0.06 0.85 rt 0.04 1.32rtO.10 58.8 f3.22 1.80f0.14 0.95 f 0.14 41.2k3.22

3.04*0.15 0.84 f 0.05 1.02 f 0.03 1.86f0.08 61.8k2.59 2.21 f0.12 1.19f0.11 38.2 f 2.59

3.04*0.15 0.71 rto.05 1.01 f0.03 1.72 &-0.08 56.6 f 2.59 2.33+0.12 1.33*0.11 43.4 f 2.59

* * * *

NS NS NS NS NS NS NS NS

NS NS NS NS

aValues are least square means f standard error. bPer kg of metabollic body weight. ‘Expressed as a percent of the energy intake. *p
subsequent photoperiod exposure. Indeed, initial exposure to 16L:8D photoperiod during weeks 1 to 6 did increase weight gain by 6.6% and feed intake by 9.5%. Peters et al. (1978, 1980) and Petitclerc et al. (1983) have observed, in dairy heifers, similar effects. However, this initial exposure (6 weeks) was sufficient in duration to prevent recognition by the animals of a subsequent photoperiod signal. Zinn et al. ( 1988) reported, in a note, that previous exposure affected the magnitude of photoperiod-induced changes in animal growth. Indeed, in heifers exposed to 8L:16D for 63 days after 3 months of age, there was no effect of

subsequent 8L:16D or 16L:8D photoperiods on liveweight gain over the next 150 days; however, in heifers initially exposed to 16L:8D and subsequently switched to 8L: 16D, liveweight gain was significantly reduced when compared to heifers continuously exposed to 16L:8D. Type and magnitude of the response to photoperiod treatment, in the study by Zinn et al. ( 1988), might have been different due to age, sex, duration of treatment and( or) time of the year at the onset of treatment. Nevertheless, our results and those of Zinn et al. ( 1988) clearly show that previous photoperiod exposure will affect the animal’s respon-

34

G. Guertin et al. /Livestock Production Science 44 (1995) 27-36

siveness to a subsequent photoperiod signal. Roche and Boland (1980), Sorenson (1983) and Zinn et al. (1986) did not observe any significant effect of photoperiod on growth performance. However, this nonresponsiveness to photoperiod might have been due to the fact that animals were already programmed to a photoperiod signal at the onset of treatment. Previous researchers have reported improved feed efficiency due to long-day photoperiod in group-fed heifers (Peters et al., 1980; Petitclerc et al., 1983). However, in this study, with individually fed animals for the first time, there was no effect of photoperiod on feed/gain ratio. Furthermore, the digestibility of the nutrients, energy and nitrogen retentions, and blood urea level were not affected by photoperiod. Eisemann et al. ( 1984) had reported that prolactin, which is influenced by photoperiod, could increase the absorptive capacity of the intestine and, consequently, increase nutrient absorption from the feed. However, in this study, there was no such effect. Mechanism of action of photoperiod in cattle is not clearly understood (Tucker and Ringer, 1982; Petitclerc and Zinn, 1991). Ingvartsen et al. (1992) have observed in cattle a positive correlation betwen voluntary dry matter intake (VDMI) and natural daylenght. Indeed, VDMI increased by 0.32% per hour increase in daylenght. Thus, long-day photoperiod will increase growth rate in cattle through an increase in feed intake. How photoperiod increased growth rate when feed intake was restricted and equal between short and long-day photoperiod groups (Petitclerc et al., 1993j remains unclear. Growth performance of animals fed whole maize, whole barley, or rolled barley based diet was compared for the first time in this study. Weight gain of calves fed whole barley was similar to those of calves fed whole maize. These results are in agreement with Kay et al. ( 1972) and Beauchemin et al. (1990) but contrary to Latrille et al. ( 1983) who observed that whole maize fed calves gained 7% more weight per day than whole barley fed calves. Nevertheless, in these experiments and our study, weight gain of whole barley fed calves was always at the expense of increased feed intake and decreased feed efficiency. The results obtained during the.first digestibility trials for whole maize diet agree with those obtained by Beauchemin et al. (1990) with calves of similar weight. Digestibility of dry matter (75.6%), energy

(75.0%) and ADF (38.8%) obtained for whole maize by Latrille et al. ( 1983) were lower than those obtained in this study (80.7, 80.0, and 63.0%, respectively), while their value for starch digestibility (97.0%) was higher compared to our results (88.6%). However, in our study, starch values were expressed free of glucose and, therefore, should be expected to be lower. Digestibility of dry matter, energy, nitrogen, starch, phosphorus, and copper but not ADF was lower for whole barley than for whole maize diet. Similar results were also obtained by Latrille et al. (1983); however, in their study, only the apparent digestibility of starch and ADF was significantly lower. Whole barley fed calves consumed 8% more feed than rolled barley fed calves. They gained a similar amount of weight and, therefore, were 10% more efficient in converting feed into gain. Apparent digestibility of dry matter was improved by 6.9%, energy by 7.4%, starch by 18.0%, phosphorus by 14.8% and copper by 24.5% in rolled barley as compared to whole barley diet. These results support the difference observed in feed efficiency. Hence, the mechanical treatment of barley (rolling) is recommanded to improve the efficiency of weight gain. Similar results have been obtained by Morgan and Campling ( 1978) and Macleod et al. ( 1972). According to Deyoe ( 1976) and Orskov ( 1979), the improvement in digestibility of nutrients was expected; surface area is increased and so is its susceptibility to rumen microorganisms and digestive enzymes. Hence, a better utilization and availability of the nutrients for the digestion (Hale, 1973) and an improved feed efficiency as reported by Hironaka et al. ( 1992) should occur. Model for predicting voluntary feed intake in cattle have been reviewed recently by Ingvartsen ( 1994). An animal will continue to eat energy until its intake capacity for energy is reached and metabolic factors limit its voluntary feed intake. Indeed, in this study, there was no difference between diets concerning digestible energy intake and energy retained even thought there were significant differences in dry matter intake between diets. Energy intake was lower for the calves fed whole maize diet than those fed both barley diets but the difference was not significant. However, calves fed whole maize diet excreted significantly less energy through feces and urine, and retained more energy when expressed as a percentage of the energy intake. Nevertheless, it appears that the animals fed both barley diets tried to compensate for a low energy digestibility

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Production Science 44 (1995) 27-36

by increasing DDMI in order to maintain daily energy retention and ADG. Blaxter (1962) reported that the efficiency of energy utilization should be reduced as ruminal starch digestion increases. Calves fed the whole barley diet may have absorbed and retained less energy because the barley starch is almost completely fermented in the rumen. Orskov (1986) found that at least 90.0% of the barley starch is fermented in the rumen but, due to a slower rate of starch digestion, up to 40.0% of maize starch can be found to escape fermentation in the rumen. Waldo ( 1975) suggested that concentrate diets that permit starch to enter the small intestine for enzymatic digestion should be more efficient than those where rumen fermentation is extensive. Calves fed whole barley diet retained less energy (64.7 vs. 69.8% as a percentage of energy intake) than those fed rolled barley diet. According to Pavlicevic et al. ( 1972), the amount of starch passing through the abomasum was greater when a diet based on whole barley (36.7%) was fed to steers compared to a diet based on rolled barley (6.4%). The most efficient utilisation of starch by the animal occurs normally when starch is digested in the small intestine. However, in ruminants, the mechanical treatment of cereal improves significantly its utilisation (Hale, 1973) even though grain starch would be mostly digested in the rumen. Nitrogen retention was not affected by diets. However, nitrogen intake and excreted were higher for both barley diets than for the whole maize diet. Furthermore, blood urea levels were higher for calves fed both barley diets than to those fed the whole maize diet. Obviously, barley fed animals, adjusting their feed intake to meet energy demand first, have exceeded their nitrogen requirements. Indeed, calves fed the whole barley based diet had a nitrogen intake (3.04 g/day when expressed per kg of metabolic weight) superior to their requirement of 1.92 g/day when expressed per kg of metabolic weight (Ensminger and Olentine, 1978). Thus, one would expect that the excess nitrogen intake would be excreted in their feces and urine. Ensminger and Olentine (1978) have also suggested that the protein in barley ( 16.8% soluble nitrogen) is more degradable in the rumen than maize (12% soluble nitrogen). This may explain in part the higher level of blood urea and urinary nitrogen in calves fed whole and rolled barley diets. The mechanical treatment of barley did not improve nitrogen absorption and retention when compared to

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whole barley diet. Indeed, nitrogen intake, excreted and retained, and blood urea level were not significantly different between calves fed the whole or rolled barley diet. In conclusion, long-day photoperiod can improve average daily gain of fast-growing grain-fed calves. However, previous photoperiod exposure of the animals will induce for several weeks a refractory period to any new photoperiodic signal. Feed efficiency of whole barley fed calves is poorer as compared to whole maize fed calves but improvement is gained by rolling barley.

Acknowledgments This research was financed in part by Agriculture and Agri-Food Canada and by the Conseil des Recherches et Services Agricoles du Quebec. The authors wish to acknowledge the assistance of Bob Suitor, Lucien Beauchemin, Denis Thibault and Jean Marceau for their work with the animals. We also wish to thank Franqois Clavet, Andre Belleau and Nicole Perreault for technical assistance in the chemical and statistical analysis, and Louise Boisvert for typing the manuscript.

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