Effects of ensiling potato hash with either whey or sugarcane molasses on silage quality and nutrient digestibility in sheep

Experiment was conducted to study the effect of whey and molasses addition on potato hash at ensiling on silage quality and nutrient digestibility in sheep. Potato hash silage was produced by mixing 800 g/kg potato hash with 200 g/kg hay, and ensiled in 210 l drums for 90 days.

Higher (P<0.05) concentrations of lactic acid and reduced pH, ammonia-N and butyric acid occurred in the whey and molasses treated silages compared to the control. Furthermore, feed intake and nutrient digestibility ere improved (P<0.05) with whey and molasses addition compared to the control.

It was concluded that feeding the potato hash silage without supplementation may lead to poor animal performance due to low dry matter content of the silage.

Introduction

Potato hash, a mixture of potato skins, starch, fats and yellow maize obtained after the production of snacks, is one of the agro-industrial by-products that is available in appreciable quantities in South Africa. This by-product contains 150 g DM/kg of fresh potato hash, 700 g starch/kg DM, 11.16 MJ ME/kg DM, 105 g CP/kg DM, 369.6 g NDF/kg DM and 162.5 g ADF/kg DM. Despite the fact that potato by-products can be processed (e.g. drying) and fed to animals (Charmley et al 2006, Tawila et al 2008), potato hash is usually fed as fresh to animals by farmers. However, this by-product is produced in high volumes, particularly during the peak periods and if it is not consumed in a short period of time by animals, it gets mouldy and becomes useless for animal feeding.

Interest in conserving by-products by ensiling is steadily increasing largely due to the increase in their use as animal feed (Megias et al 1998, Kayouli and Lee 1999, Bakshi et al 2006, Kholif et al 2007). It has been reported that through proper ensiling, silage from high moisture by-products can replace costly feeds such as maize silage in ruminant diets (e.g. Itavo et al 2000, Lallo et al 2003, Pirmohammadi et al 2006). To successfully ensile potato hash, substantial amounts of fermentable sugars are required to produce lactic acid to lower the pH and stabilize the product (McDonald 1981, Wilkinson 2005). Some researchers (Megias et al 1998, Kholif et al 2007) successfully ensiled food by-products with chemical additives and reported improved fermentation quality and digestibility of the silages. However, a constraint with chemical additives is that they are corrosive to the equipment used and can be dangerous to handle, and biological additives are therefore preferred (Gwayumba 1997). Biological additives can be costly to the farmer and their effectiveness can be less reliable, since it is based on the activity of living organisms (Weinberg and Muck 1996). Alternatively, food waste materials such as whey (Bautista-Trujillo et al 2008, Nkosi 2003, Zobell et al 2004) and sugarcane molasses (Yunus et al 2000, Van Niekerk et al 2007, Nkosi et al 2009) can be used as silage additives. Literature pertaining the ensiling of potato hash with whey and molasses is limited. The present study was therefore done to evaluate the fermentation of potato hash silage produced with or without additives (whey and molasses), and its effects on feed intake and nutrient digestibility in sheep.

Materials and methods

Potato hash was collected from Simba, a food producing factory in the Gauteng Province and brought to the ARC-Irene Institute, South Africa (longitude 28⁰ 13`S : latitude 25⁰ 55`E, altitude 1524 m) for chemical analysis, silage making and nutrient digestibility experiment. Potato hash silage was produced by mixing 800 g/kg potato hash with 200 g/kg hay (as is basis) and treated with: control (no additive), whey and molasses. Where molasses was used, it was diluted with warm water at a ratio of 1:2 (4 h before application), and was sprayed over the material at a theoretical application rate of 30 l per ton fresh material (FM). Whey was sprayed at 30 l per ton fresh materials to obtain at least > 10⁶ cfu/g FM. In order to add the same amount of moisture as with the treated silages, the control was sprayed with 30 l of distilled water over a ton of fresh material. The materials were ensiled in 210 l drums that were lined with plastic bags and were closed with a rubber lid to prevent damages to the bags by rodents. After 90 days of ensiling, the drums were opened and samples were collected and analysed for chemical composition and fermentation characteristics as described by Nkosi et al (2009).

The silages were fed to 9 matured South African Dorper sheep (43.5 kg ± 0.214 live weight) in a 3 x 3 Latin square experimental design for 30 d. The sheep were randomly assigned to treatment in each period (10 d, i.e. 5 d adaptation and 5 d faecal collection periods) with the condition that no sheep received the same treatment thrice. There were 3 sheep per treatment per period. Sheep were fitted with leather harnesses and canvass bags attached to the back of each sheep 3 days before the digestion trial started. Daily feed intake and faecal outputs were recorded. Faeces accumulated for the 5 days period were pooled per sheep and sub-samples were collected for the determination of chemical composition and saved frozen. The data on the differences between treatment means for the fermentation, chemical composition, and digestibility were analysed in a completely randomized design by the analysis of variance (ANOVA) using Genstat (2000). Significant statistical differences between the means were declared when probabilities (P) were below 0.05.

Results and discussions

Silage fermentation characteristics

Data on the chemical composition and fermentation characteristics of the silages is presented in Table 1.

Table 1. Chemical compositions and fermentation characteristics of pre-ensiled and ensiled potato hash after 90 days of ensiling (n = 3)
	Pre-ensiled	Control	MPHS	WPHS	SEM
DM , g/kg	250	232^a	236^a	230^b	0.530
Ash, g/kg DM	59.4	60.4^a	55^b	61.1^a	1.81
CP, g/kg DM	89.1	72.3^c	82.5^b	86.0^a	0.003
CF, g/kg DM	259	334^a	303^b	275^c	0.4
EE, g/kg DM	72.7	45^a	37^b	34^c	0.283
ME, MJ/kg DM	10.9	7.8^b	9.6^a	9.7^a	0.05
pH	4.78	4.5^a	4.2^b	4.3^b	0.01
WSC, g/kg DM	22	13.3^b	16.5^a	14.5^a	0.27
LA, g/kg DM		26.1^c	47.5^a	42.5^b	0.18
AA, g/kg DM		28.5^a	21.0^c	23.5^b	0.26
PA, g/kg DM		6.3^a	6.7^a	5.2^b	0.88
BA, g/kg DM		0.91^a	0.42^c	0.52^b	0.03
NH₃-N as %TN		1.38^a	1.15^b	1.15^b	0.09
^abc Means with different letters in a row differ significantly (P<0.05) MPHS; molasses potato hash silage, WPHS; whey potato hash silage, LA; lactic acid, WSC; water-soluble carbohydrates, AA; acetic acid, PA; propionic acid, BA; butyric acid, TN; total nitrogen

Water-soluble carbohydrates are regarded as essential substrates for the growth of LAB for proper fermentation, and low levels may restrict LAB growth (McDonald et al 1991). According to Haigh and Parker (1985), a concentration of 30 g/kg DM of WSC in a herbage is critical for a successful fermentation. The concentration of WSC in the potato hash mixture at pre-ensiling was 22 g/kg DM, indications that it was not enough for efficient fermentation. This warranted the addition of whey and molasses to improve the fermentation process.

The pH of the silages after 90 days of ensiling was reduced to 4.5 for the control and 4.3 for the MPHS and WPHS respectively. However, the pH of the control was not low enough for efficient preservation because it should be 4.20 or 4.35 at a DM content of 200 and 250 g/kg (Weissbach 1968) and only the whey and molasses treated silages reached this target. The results further revealed that whey and molasses addition increased (P<0.05) the concentration of lactic acid, reduced silage pH and the concentrations of butyric acid and ammonia-N compared to the control, indications of well-preserved silages (McDonald et al 1991). This confirmed previous work that reported higher lactic acid concentrations, lower pH and ammonia-N content when molasses (Yunus et al 2000, Nkosi et al 2009) and whey (Bautista-Trujillo et al 2008, Zobell et al 2004) were added to a forage at ensiling compared to the control. Moreover, whey and molasses addition reduced (P<0.05) the fibre content of the silage as compared to the control, which could be attributed to partial hydrolysis of hemicelluloses in the treated silages (Muck and Kung 1997). This agreed with Fazaeli et al (2003) who reported a decrease in fibre content in liquid whey treated straw silage, and Guney et al (2007) in molasses treated sorghum silage compared to the control.

Ammonia-N in silage reflects the degree of protein degradation (Wilkinson, 2005), and well-preserved silages contain less than 100 g NH₃-N/kg TN (McDonald et al 1991). The silages in the present study had ammonia-N concentrations of less than 100 g NH₃-N/kg TN. However, treating potato hash silage at ensiling with either whey or molasses reduced (P<0.05) the ammonia-N concentration compared to the control, supporting the work of other researchers (Yunus et al 2000, Bautista-Trujillo et al 2008, Nkosi et al 2009). This can be explained by the fact that whey and molasses reduced the pH resulting in a decreased production of NH₃-N in the silage compared to the control. The higher concentration of NH₃-N in UPHS led to a decrease in the CP content of the silage compared to the other silages. Nevertheless, the CP concentrations of the silages were within the range of 72 – 89 g/kg DM of CP typically found in silages (McDonald 1981).

Higher (P<0.05) concentration of butyric acid occurred in the UPHS, leading to a reduced energy content of the silage compared to the other silages. It is well established that adding molasses and whey reduced the concentration of butyric acid in silage (Bautista-Trujillo et al 2008, Nkosi et al 2009). A concentration of < 0.1 g/kg DM butyric acid is typical found in well preserved silage (Kung and Shaver 2001). The ME content in the MPHS and WPHS is within the range of 9.6 – 12.2 ME MJ/kg DM typically found in silages (Wilkinson 2005). The reduced ME in the control might be attributed to the high butyric acid content, which is an indication for the loss of energy in the silage (McDonald 1981).

Silage intake and digestibility

It is well established that feed intake is more likely to be lower when ruminants are fed solely on silage, and poor animal performance can be expected (Fitzgerald 1986). The sheep recorded DMI of < 700 g/d which warranted the need for supplementation to achieve a better lamb performance. Higher lamb performance can be achieved if the DM of silage is > 300 g/kg (Phipps and Wilkinson 1985, cited by Meeske 2001), and the silages in the present had DM content of < 250 DM g/kg (Table 1). Data on the intake and digestibility of potato hash silages by sheep is shown in Table 2.

Table 2. Mean values for the feed intake (g/d) and digestibility of potato hash silages by lambs (n = 3)
	Control	MPHS	WPHS	SEM
Intake, g/day
DM	619^b	681^a	684^a	44.0
OM	609^b	658^a	653^a	41.9
CP	45.2^b	56.5^a	54.3^a	6.60
EE	27.9^a	25.2^b	21.5^c	1.44
ADF	198^b	209^a	202^a	11.0
NDF	2849^b	306^a	289^a	13.3
Apparent digestibility, %
DM	49.30^b	59.31^a	58.10^a	3.59
OM	48.95^b	60.47^a	59.51^a	0.265
CP	40.4^b	59.7^a	65.3^a	4.32
EE	70.0^c	77.1^b	86.3^a	2.26
ADF	40.1^b	57.1^a	60.5^a	5.53
NDF	43.0^b	58.8^a	62.8^a	5.26
^abc Means with different letters in a row differ significantly (P<0.05) UPHS; untreated potato hash silage, MPHS; molasses potato hash silage, WPHS; whey potato hash silage, SEM; standard error of means

The results show that there were differences (P<0.05) in the intake of silages by sheep, which could be attributed to variations in the chemical composition and fermentation end products of the silages (Wilkinson et al 1971, Kriszan and Randby 2007). Higher (P<0.05) intake of DM, OM, CP and fibre (ADF and NDF) were obtained in the MPHS and WPHS compared to the control. This supported the work of other researchers who reported that whey addition (Khattab et al 2000) and molasses (Baytok et al 2005) to forage at ensiling improved silage intake compared to the control.

Moreover, the voluntary intake of silage has been found to correlate positively with CP concentration and negatively with ammonia-N concentration (Kriszan and Randby 2007, Wilkinson et al 1971). Higher CP contents in final silages are required for adequate intakes, and any reduction in the CP content during the fermentation of forage may adversely impact intake (Wilkinson 2005). The WPHS and MPHS silages had lower (P<0.05) concentrations of ammonia-N and butyric acid, and had higher (P<0.05) CP content compared to the control, and were most preferred by the sheep compared to the control.

Forage fibre (ADF and NDF) content has been regarded as an important factor in the regulation of forage intake (Meissner 1999, Van Soest et al 1991). The control had higher (P<0.05) fibre contents than the other silages, which might be one of the reasons for its lower DM, OM and CP intakes. Whey and molasses addition reduced (P<0.05) the fibre content of the silage as compared to the control, which could be attributed to partial hydrolysis of hemicelluloses in the treated silages (Muck and Kung 1997). This agreed with Fazaeli et al (2003) who reported a decrease in fibre content in liquid whey treated straw silage, and Guney et al (2007) in molasses treated sorghum silage compared to the control. Both studies recorded improved digestibility of DM and OM compared to the control. Moreover, Khattab et al (2000) reported improved nutrient digestibility from whey treated banana waste silage compared to the control which is in agreement with the present study. In contrast, Zobell et al (2006) did not observe improvements in the digestibility of DM when liquid whey was added to wheat straw and wheat middlings at ensiling compared to the control. The lower digestibility of DM, OM and higher concentrations of ammonia-N and EE in the control might have contributed to the low preference for this silage. Moore et al (1986) reported a depressed digestibility of fibre when a diet containing higher fat was fed to steers.

It can be concluded that whey and molasses addition to potato hash at ensiling improved its acceptability and nutrient digestibility in lambs compared to the control. Feeding the silage without supplementation may lead to poor animal performance due to its lower DM content, and the silage is therefore recommended to ruminants for body maintenance especially during the periods of feed scarcity.

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