Optimum cassava root chip levels in lactating cow diets

 C Wachirapakorn, M Wanapat, N Sornsungnern and S Kowsuwan* 

Department of Animal Science, Faculty of Agriculture,
Khon Kaen University, Khon Kaen 40002, Thailand
* NaKhonsawan Agriculture and Technology College, 
Nakhonsawan, 6000, Thailand

Abstract

This experiment was aimed at studying the effect of cassava root chip levels in concentrates on milk yield in lactating cows. Eight lactating cows (four 50% Holstein-Friesian (HF) and four 75% Holstein-Friesian), with an average weight of 390+27.5 kg and 141+43.5 days in milk, were used in a replicated 4x4 Latin square design with 21 day periods. The cows were fed ad libitum a ration consisting of roughage (dried Ruzi grass) and concentrate at a ratio of 30 to 70. There were four levels of cassava root chips: 25, 35, 45 and 55% in the concentrate.

The levels  of cassava root chips in the concentrate did not have any effect on total dry matter intake, digestion coefficients of DM and OM, 3.5% fat-corrected milk yield and milk composition. The , 3.5% FCM yield in the 50% HF cows (10.0±0.19 kg/d) was higher (P<0.01) than that in the 75% HF cows (8.41±0.19 kg/d).

In conclusion, cassava chips can be used at a high level (55%) in concentrates for dairy cow diets, and 50% HF crosses can produce more milk than 75% HF cows in the same environment and on the same diet.

Key words: Milk, Holstein crosses, cassava root chips, dairying

Introduction

Dairy production in Thailand is developing dramatically, with the number of cows increasing from 287,144 to 474,090 head over the last five years, and with an average milk yield of 11.0 kg/d (Uraikul 1998). However, most of the dairy cattle raised are Holstein crossbreds, ranging from 65 to 75% Holstein. The Division of Animal Breeding (1987) reported that 50% Holstein crossbred cows produce on average 1,811 kg per lactation (248 days), which is lower than that observed by Simarak (1989). This  author reported that 75% Holstein crossbreds produced 3,054 kg per lactation, while cows with less than 75% Holstein produced 2,873 kg per lactation, averaging seven lactations. As the proportion in Holstein blood increases, the requirement for nutrients also increases if they are to achieve their potential milk production, and thus feeding high producing dairy cows needs to be considered carefully, particularly when using crop residues as roughage sources.

The current market price of cassava (Manihot esculenta, Crantz), which has been widely grown in Thailand for many years, is low, and one option to increase its value is to use it in dairy diets as an energy source in order to reduce the concentrate price. Cassava root chips contain 88-90% dry matter (DM), 2.3-2.5 % crude protein (CP) and 76-81% soluble carbohydrate (Gomez and Waldivieso 1983).

Sathapanasiri et al (1990) observed that starch of cassava is highly degraded in the rumen (94%) and completely digested in the whole tract. A similar result has been reported by Sommart et al (1991). Although cassava root chips are known to be a good  energy source in dairy cow diets, the optimal level has not been determined. Therefore, the objective of this experiment was to study the effect on performance of different levels of cassava root chips in concentrates and to compare milk production between 50% and 75% Holstein cows.
 

Materials and Methods

Eight lactating Holstein-Friesian (HF) crossbred cows (390±27.5 kg) in mid lactation (141±43.5 days) were assigned to receive one of four dietary treatments in a replicated experiment with a 4x4 Latin square design with 21 day periods. One square consisted of four 75% H F crossbred cows and the other square consisted of four 50% H F crossbred cows. The dietary treatments were levels of cassava root chips of: 25, 35, 45 and 55% in the concentrates (Table 1). 

The cows were fed individually twice daily (07.00 and 15.00 h) in equal allotments an amount to achieve ad libitum intakes (about 10% refusals). Diets were adjusted as necessary to maintain the 30:70 ratio of dried Ruzi grass (Brachiaria ruziziensis) to concentrate. The diets were formulated to meet NRC (1989) requirements for 400 kg cows yielding between 6 to 13 kg/d of milk. Amounts fed were recorded daily and sampled weekly for component analysis. Composites of weekly samples were analyzed for DM (105 ºC for 24 h), ash (550 ºC for 8 h) , CP (Kjeldahl procedure using Tecator Kjeltec, Tecator, Inc., Herndon, VA), and neutral-detergent fiber (NDF) and acid-detergent fiber (ADF) according to the method of Goering and Van Soest (1970). Digestibility of DM, organic matter (OM) and NDF was estimated using acid insoluble ash (AIA) as an internal unabsorbable marker (Van Keulen and Young 1977). Fecal samples taken by rectal sampling were collected during the last 4 d of each experimental period and then composited for component analysis as per the feed samples.

Milk production was recorded at each milking. Milk was sampled on two consecutive milkings for composition analysis. Milk fat, protein, lactose and solids-not-fat (SN F) contents were determined by Milkoscan 33 (Foss Electric, Denmark). Body weights were recorded immediately following the morning milking at the beginning and end of each period. Rumen fluid, taken 4 h post-feeding by stomach tube, was measured immediately for pH and then preserved by 6 N HCl for later determination of NH3-N concentration (Bremmer and Keeney 1965).

Data were summarized and analyzed as a replicated 4x4 Latin square using the general linear models procedure of SAS (1985). The model included diet, period, cows within square and the interactions of square by treatments were sources of variation. The linear model used is described by the following equation:

Yijk = m + Si +Cj(i) + Pk + Tl + (ST)il+ Eijkl

where

m = overall mean, Si = effect of square i, Cj(i) = effect of cows j, Pk = effect of period k, Tl = effect of treatment l, (ST)il = square x treatment interaction, and Eijkl = experimental error.

The effect of dietary treatments was expressed as least square means. Duncan’s New Multiple Range Test was used to compare dietary effects. Significance was at P<0.05. Pooled standard errors are reported for all data.

Results and Discussion

The chemical composition of dried Ruzi grass and the concentrates used in the experiment is shown in Table 1. The crude protein content of the concentrates was similar among dietary treatments, ranging from 19.9 to 21.1%. Daily dry matter intake and digestion coefficients of DM and OM did not differ among dietary treatments nor between breeds (Table 2).  

The level of cassava root chips (55% in the concentrate or 38% of total diet) was higher than reported previously by Sommart et al (1996), who suggested  that the optimal level of cassava root chips wass between approximately 20 and 30% in the total diet. Increases in the level of cassava root chips in the concentrate did not affect (P>0.05) rumen pH and NH3-N concentration measured 4 h post-feeding (Table 3). However, rumen pH was at an optimal level for activity of cellulolytic bacteria (Wanapat 1990). Although the concentration of NH3-N was lower than that reported by Sommart et al (1996), the concentration found in this study was above the minimum concentration (50 mg NH3-N/litre) considered to be non-limiting for microbial growth in the rumen reported by Satter and Slyter (1974). 

Milk production and milk composition were not different (p>0.05) among treatments, but milk production and 3.5%FCM were significantly higher (p<0.01) in the 50% HF cows than in the 75% HF cows (Table 4). This result is in accordance with the results of the Division of Animal Breeding (1987). The lower milk production of the 75% HF cows was probably due to the environmental conditions. The high temperatures (30-40 ºC) and humidity (65-79%) during the experiment could have resulted in the development of heat stress in the 75% HF cows (Armstrong 1994), and consequently decreases in intake, digestibility and production, when compared to the 50% HF cows. 

Conclusions

• Cassava root chips can be used as an energy source in lactating cow diets at very high levels (55% in concentrate or 38% of total diet), without affecting feed intake, milk production and milk composition.
• 75% HF cows produced less milk than 50% HF cows when fed the same diet.

Acknowledgements

The authors acknowledge the National Research Council for providing financial support and the Department of Animal Science, Faculty of Agriculture, Khon Kaen University for providing the animals and laboratory facilities.

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