Effects of feeding rapeseed products on voluntary roughage intake and nutrient digestibilities in dairy cows

Dietrich Philipczyk¹, Karl-Heinz Südekum¹, Manfred Brandt¹

and Klaus Pabst²

¹Institute of Animal Nutrition, Physiology and Metabolism, University of Kiel, 24098 Kiel, Germany, e-mail: suedekum@aninut.uni-kiel.de, and ²Institute of Chemistry and Physics, Federal Dairy Research Centre, P.O. Box 6069, 24121 Kiel, Germany

Abstract

Fourty-two lactating dairy cows were utilized in a balanced two-period changeover design to determine the effects of inclusion of rapeseed fat in concentrates on voluntary roughage intake and whole-tract nutrient digestibilities. Periods were five weeks with samples collected during the last week. In the experimental concentrates, wheat was isoenergetically replaced with two levels of fat (ether extract). Fat from rapeseed (0.275 or 0.550 kg cow^-1 day^-1 ) was included either in the physical form of ground rapeseed or as rapeseed oil plus rapeseed expeller. In addition, whole rapeseed was pelleted together with soyabean meal (0.550 kg fat cow^-1 day^-1). Cows were fed wheat silage for ad libitum intake and 4.4 kg of dry matter (DM) day^-1 of maize silage. Daily intakes by cows of silage (14 kg) and total diet DM (19 kg) were not different (P > 0.05) among diets. Organic matter (OM) and crude protein (CP) digestibilities were two percentage units lower when the diets contained rapeseed fat in either form. Contrarily, fat digestibilities were higher (P < 0.05) for the diets containing 0.550 kg of additional fat (mean, 66.8%) than for the diets containing no fat or only 0.275 kg of additional fat (mean, 60.9%). Although cows on all diets consumed large quantities of starch (3.5 to 4.3 kg per day), which should make animals susceptible to drastic manipulations of their ration, the inclusion of rapeseed fat in either physical form and inclusion level had no negative effects on DM intake and only small effects on nutrient digestibilities. When high quality roughage is offered for ad libitum intake, rapeseed fat of different physical forms can be included in diets of dairy cows without negatively affecting intake and digestion.

Keywords: oilseeds, fat supplementation, physical form, whole-crop silage, starch, fibre

Introduction

Oilseeds are a convenient source of both fat and protein to improve the energy balance of dairy cows. Dietary fat may reduce feed intake (Hagemeister and Kaufmann, 1979) and ration fibre digestibility as well as milk fat and protein content (Palmquist and Jenkins, 1980; Wu and Huber, 1994) but it may change the milk fat composition to allow the production of a softer, more spreadable butter (Banks and Christie, 1990) with elevated concentrations of mono- and polyunsaturated fatty acids. Because the inclusion in diets for dairy cattle of high amounts of maize silage or whole-crop silage, produced from small cereal grains, reduced the spreadability of butter fat in the Northern parts of Germany, oilseeds, and in particular home-grown rapeseed, could be an attractive dietary ingredient.

Although numerous authors have reported on effects of rapeseed or canola on milk fat composition (for review, see Grummer, 1991; Kennelly, 1996; Kennelly and Glimm, 1998), the physical forms and proportions at which rapeseed may be included in rations to obtain elevated levels of mono- and polyunsatured fatty acids without negatively affecting nutrient digestibilities and milk constituent yields have not been established clearly. Therefore, the overall objective of this study was to determine how milk fat composition can be altered by different physical forms and amounts of rapeseed in diets fed to dairy cows towards a softer, more spreadable butter without negative effects on milk constituent contents and yields and on intake and digestion characteristics. In this paper, we report on dry matter (DM) and nutrient intakes and on whole-tract nutrient digestibilities.

MaterialS and Methods

Fourty-two midlactation Holstein dairy cows were utilized in a balanced two-period changeover design (Gill and Magee, 1976). Animals wer randomly assigned to one of seven treatments; six treatments are included in this paper. The control (CON) concentrate consisted of (g kg^-1 DM) 260 wheat, 530 soybean meal, 130 rapeseed meal, 60 mineral-vitamin mix, and 20 molasses. In the experimental concentrates, wheat and rapeseed meal were partially replaced with two levels of different rapeseed (Brassica napus, double-low, autumn-sown variety Ceres) products. Fat (ether extract) from rapeseed (0.275 and 0.550 kg cow^-1 day^-1) was included in form of rapeseed that was ground with a hammer-mill to pass a 3-mm sieve (G275 and G550) or as rapeseed oil plus rapeseed expeller (O275 and O550). In addition, whole rapeseed was pelleted with soybean meal (0.550 kg fat cow^-1 day^-1 , P550). All concentrates were isonenergetic and contained TiO₂ (20 g cow^-1 day^-1 ) as an inert digestibility marker. Cows were offered whole-crop wheat silage for ad libitum intake (5 to 10% refusals) and 4.4 kg of maize silage DM day^-1. Concentrates and roughages were offered four- and two-times daily, respectively. The chemical composition of the feeds is given is Table 1.

Table 1. Chemical composition of dietary ingredients (% of dry matter)

Ingredient	Crude protein	NDF	ADF	Starch	Fat^1	Ash
Roughage type
Maize silage	9.3	50.1	24.5	25.5	3.0	4.3
Wheat silage	8.2	48.7	27.6	24.5	2.0	4.0
Concentrate type^2
CON	35.0	17.6	8.9	17.7	2.8	9.6
G275	36.6	17.0	10.0	11.6	7.2	10.1
G550	35.5	13.6	10.9	2.1	13.1	11.0
O275	36.8	17.0	9.7	9.4	7.2	10.5
O550	38.0	15.6	11.0	1.5	13.3	11.6
P550	38.2	13.2	10.0	1.3	14.8	11.2

¹ Acid-ether extract.

² CON = Control; G275 and G550 contained 275 and 550 g fat from ground rapeseed; O275 and O550 contained 275 and 550 g fat from rapeseed oil plus rapeseed expeller; P550 contained 550 g fat from pelleted whole rapeseed.

Periods lasted 35 days and data were collected during the last week of each period. Feed samples were collected daily and vacuum-packed for subsequent analyses. Before the morning feeding, refusals of each cow were weighed, recorded and vacuum-packed. Faecal grap samples were collected twice daily around feeding times and stored at –20°C. Feed, orts and faecal samples were composited across cow within period and a representative sample of each composite was analysed for DM, ash, crude protein (CP), fat (acid-ether extract; Naumann and Bassler, 1976), and TiO₂ (Brandt and Allam, 1987). The NDF, ADF (Goering and Van Soest, 1970) and starch (Brandt et al., 1987) concentrations were determined in samples of refusals and faeces which were pooled across periods and treatments. Intake and organic matter (OM) digestibility data were analysed by analyses of variance using the general lienar models procedure of SAS (1982). Effects of treatments (diets) were separated further by the following orthogonal contrasts: CON versus (G275 + O275), (G275 + O275) versus (G550 + O550), (G275 + G550) versus (O275 + O550), and O550 versus P550.

RESULTS and Discussion

In general, cows consumed their concentrate portions within 30 minutes. Unfortunately, it was impossible to separate maize silage from wheat silage in refusals but the two feeds were similar in chemical composition (Table 1) and therefore were combined as total roughage refusal. Total silage (maize plus wheat) intake accounted for more than 70% of total DM intake and was not different (P > 0.10) among diets (Table 2).

Table 2. Daily intakes (kg) by cows fed diets containing rapeseed products of different physical forms and at different inclusion levels

Diet^1	Roughage dry matter	Concentratedry matter	Total dry matter	Crude protein	Starch	NDF^2	Fat
CON	13.7	5.6	19.3	3.10	4.31	7.72	0.48
G275	14.2	4.9	19.1	3.01	3.95	7.72	0.68
G550	14.1	4.8	18.9	2.83	3.53	7.62	0.94
O275	14.1	5.1	19.2	3.05	3.89	7.77	0.68
O550	14.0	4.7	18.7	2.91	3.45	7.57	0.93
P550	14.1	4.7	18.8	2.94	3.48	7.51	1.00
Significance of contrasts^3 (P <)
CONT1	NS^4	0.01	NS	NS	0.01	NS	0.01
CONT2	NS	0.05	NS	0.01	0.01	NS	0.01
CONT3	NS	NS	NS	0.1	NS	NS	NS
CONT4	NS	NS	NS	NS	NS	NS	0.01

¹ Diets are designated according to their concentrate portion: CON = Control; G275 and G550 contained 275 and 550 g fat from ground rapeseed; O275 and O550 contained 275 and 550 g fat from rapeseed oil plus rapeseed expeller; P550 contained 550 g fat from pelleted whole rapeseed.

² Neutral detergent fibre.

³ Orthogonal contrasts: CONT1 = CON versus (G275 + O275); CONT2 = (G275 + O275) versus (G550 + O550); CONT3 = (G275 + G550) versus (O275 + O550); CONT4 = O550 versus P550);

⁴ Not significant.

These results are in common with data on roughage intake by dairy cows fed sunflowerseed (Rafalowski and Park, 1982) or cottonseed (DePeters et al., 1985). In contrast, Murphy et al. (1990) determined reduced grass silage intake when ground rapeseed was fed to dairy cows. These contrasting results indicate that intake responses to oilseed supplementation may vary with oilseed and roughage sources. Total DM, OM, NDF, and ADF (data not shown) intakes were similar (P > 0.1) among diets. The fat contents of the intake DM were 2.5, 3.6, 5.0, 3.5, 5.0, and 5.3% for CON, G275, G550, O275, O550, and P550, respectively. Increasing the amount of rapeseed fat in the diet reduced starch and CP intakes.

Nutrient digestibility estimates based on faecal grab samples and TiO₂ as a marker are presented in Table 3. Feeding rapeseed fat reduced whole-tract digestibilities of OM (P < 0.1) and CP (P < 0.05), though the magnitude of the reduction was not very great. These observations are consistent with those reported by Murphy et al. (1987, 1990). In contrast, Kennelly (1983) determined higher digestibilities by feeding rapeseed and rapeseed oil. Fat supplementation increased total dietary fat digestibility. This observation can be attributed to the dilution of metabolic faecal fat with a dietary fat of high true digestibility. Starch digestibility values were high (> 97%) and similar among diets. With the exception of the G275 diet, NDF and ADF digestibilities were lower for cows fed the diets containing rapeseed fat. Palmquist and Jenkins (1980) noted that fat often caused depressed fibre digestibilities. Although in this experiment fibre digestibility values of the diets containing rapeseed were up to 9 percentage units lower than those of the control diet, this did not result in a large depression of OM digestibilties.

Conclusions

Although cows on all diets consumed large quantities of starch (3.5 to 4.3 kg per day), which should make animals susceptible to drastic manipulations of their ration, the inclusion of rapeseed fat in either physical form and inclusion level had no negative effects on DM intake and generally only small effects on nutrient digestibilities. When high quality roughage is offered for ad libitum intake, rapeseed fat of different physical forms can be included in diets of dairy cows without negatively affecting intake and digestion.

Table 3. Whole-tract digestibilities of organic matter and organic matter constituents in dairy cows fed diets containing rapeseed products of different physical forms and at different inclusion levels

Diet^1	Organic matter	Crude protein	Fat	Starch	NDF^2	ADF^3
CON	74.8	75.2	60.2	98.3	61.6	58.4
G275	75.0	75.0	63.4	98.6	62.7	59.4
G550	71.4	72.3	63.8	97.7	57.3	55.7
O275	71.1	71.3	59.2	98.2	53.0	49.5
O550	73.0	74.9	68.2	98.6	57.0	55.6
P550	71.0	72.7	68.5	98.5	55.0	53.7
Significance of contrast^4
CONT1	0.1	0.05	NS^5
CONT2	NS	NS	0.05
CONT3	NS	NS	NS
CONT4	NS	NS	NS

¹ Diets are designated according to their concentrate portion: CON = Control; G275 and G550 contained 275 and 550 g fat from ground rapeseed; O275 and O550 contained 275 and 550 g fat from rapeseed oil plus rapeseed expeller; P550 contained 550 g fat from pelleted whole rapeseed.

² Neutral detergent fibre.

³ Acid detergent fibre.

⁴ Orthogonal contrasts: CONT1 = CON versus (G275 + O275); CONT2 = (G275 + O275) versus (G550 + O550); CONT3 = (G275 + G550) versus (O275 + O550); CONT4 = O550 versus P550).

⁵ Not significant

AcknowledgEments

This study was supported by the H. W. Schaumann Foundation (Hamburg, Germany). We thank Dr. M. Strache for help with preparing the concentrate mixtures, I. Hoffmann and M. Jürgensen for skilled experimental and analytical assistance, and Dr. G. Rave for statistical advice.

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