Influence of levels of DL-malic acid supplementation on milk production and composition in lactating Pelibuey ewes and pre-weaning weight gain of their suckling kids

Abstract

Fifteen hair Pelibuey ewes were allotted individually to examine the effect of DL-malic acid (MA) supplementation level (0, 2 and 4 g of MA/kg of feed) during the first weeks of lactation on feed intake, milk yield and composition and pre-weaning weight gain of their suckling kids. Milk yield (P = 0.04) and milk efficiency (P = 0.03) increased linearly as MA supplementation increased, but dry matter intake (DMI) and milk composition (percentage of total solids, protein and fat) were not affected (P > 0.05). Increases on milk yield with no effect on milk composition led to a greater (linear effect, P = 0.02) milk protein yield. The ingestion of MA by the ewes resulted in a greater (linear, P < 0.01) average daily gain of their kids. Supplementation with 4 g of DL-ML per kilogram of feed increased milk production, milk protein yield and milk efficiency with no effect on DMI and milk composition. This milk production increase led to a greater daily gain of pre-weaned kids fed with milk as the unique feed source.

Keywords:

• early lactation
• hair breed ewes
• malic acid
• milk efficiency
• pre-weaned lambs

1. Introduction

Milk production during the first weeks of lactation is the most important factor that affects the weight gain and survival rate of kids (Snyman 2010; Gavojdian et al. 2013). When the high-quality forage is scarce, high-energy rations must be employed to maintain high yield of milk production during the first weeks of lactation. In general, increasing dietary supply of fermentable grain starch is associated with increased organics acids (mainly lactate) with the reduction of ruminal pH, increasing the risk of digestive disturbances which could affect milk production. Malate [the ionised form of malic acid (MA)] have shown that stimulates lactate utilisation by Selenomonas ruminantium (Evans & Martin 1997). Carboxylic acid salts activate the transformation of lactic acid into propionic acid through the S. rumnantium bacteria by using the succinate-propionate pathway (Martin et al. 2000); propionic acid is an essential substratum for glucose and lactose synthesis, and in this way, malate supplementation has shown increases in the ruminal pH (Montaño et al. 1999), microbial protein synthesis (Evans & Martin 1997) and available energy for growth and for milk production (Martin & Streeter 1995). Consequently, in some studies (Khampa & Wanapat 2006; Sniffen et al. 2006; Wang et al. 2009), malate supplementation had shown positive effects on milk yield and milk composition (Sniffen et al. 2006; Alcañiz et al. 2011) when added to lactating dairy cows diets. However, positive effects on milk production or milk composition have not been consistent in lactating cows (Martin et al. 2000; Vicini et al. 2003) and goats (Salama et al. 2002). Inconsistency in the effects of malate supplementation is attributed mainly to the composition of diet and/or MA dose (Wang et al. 2009). Since very limited information is available regarding the effects of malate supplementation in non-dairy lamb breeds, which have lower milk production than the dairy goats, therefore, this trial was performed to evaluate the effect of supplementation level of DL-MA in Pelibuey ewes fed a total mixed ration (high-energy) on milk production and composition and average daily gains in their suckling kids during the first weeks of lactation.

2. Materials and methods

All animal management procedures were conducted within the guidelines of locally approved techniques for animal use and care (NOM-051-ZOO-1995: humanitarian care of animals during mobilisation of animals; NOM-062-ZOO-1995: technical specifications for the care and use of laboratory animals). Livestock farms, farms, centres of production, reproduction and breeding, zoos and exhibition hall must meet the basic principles of animal welfare (NOM-024-ZOO-1995: animal health stipulations and characteristics during transportation of animals).

2.1. Animals and sampling

Fifteen multiparous Pelibuey ewes (50.80 ± 6.86 kg BW and 3.2 ± 2 body condition score) were selected from a commercial flock and were allotted in individual pens with automatic waterers and individual feeders. One week before lambing, ewes were assigned to the individual pens and were adapted to the basal diet. The trial began one week after lambing and lasted four weeks. On the third day of the first week before the start of the experiment, the ewes were milked in order to familiarise them with milking management. Three treatments were assigned randomly (5 ewes/treatment): (1) No MA supplementation (MA₀), (2) 2 g of MA/kg of feed (MA₂) and (3) 4 g of MA/kg of feed (Table 1). MA was purchased from Sigma-Aldrich Chemical Company (St. Louis, MO). The supplemental levels of MA were assigned based on those used in the previous experiments (Salama et al. 2002; Sniffen et al. 2006). Animals were fed ad libitum once a day at 0800 h. Daily feed allotments to each ewe were adjusted to allow minimal (<5%) feed refusals in the feed bunk. The amounts of feed offered and feed refused were weighed daily. Feed bunks were visually assessed between 0700 and 0720 h each morning, refusals were collected and weighed, and feed intake was determined. Adjustments to, either increase or decrease, daily feed delivery were provided daily. Feed and refusal samples were collected daily for dry matter (DM) analysis, which involved oven-drying the samples at 105°C until no further weight loss occurred (AOAC 2000). Basal diet was prepared weekly. A batch was divided into three parts, and MA was added according to the treatments. Milk yield and milk composition and body weight changes of lambs were registered weekly as follows: all ewes were separated from their lambs approximately at 0800 h once a week. Ewes received an intramuscular (IM) injection of 5 IU of oxytocin (Oxitocina 20UI, Virbac de México, Guadalajara, México) and were milked immediately with a milking machine (portable milking machine, model TJAL-151-E, Ordemex, Aguascalientes, México). A second IM injection of 5 IU of oxytocin was given and milking was repeated to ensure that as much milk as possible was removed from the udder. After 4 h (approximately 1200 h), ewes were milked again following an IM injection of 5 IU of oxytocin. The volume of milk was recorded (within 50 mL) using milk metres fitted with goat nozzles (Afimilk, model AfiFree 155, Afikim kibutz, Israel) and used to calculate daily milk production. The lambs were weighed (electronic scale; TORREY TIL/S: 107 2691, TOR REY electronics Inc, Houston TX, USA) between 1230 and 1300 h and returned immediately to their mothers after milk collection.

Table 1. Ingredients and chemical composition of basal diet.

Item	MA0	MA2	MA4
Ingredient (% of DM basis)
Cracked corn	45.50	45.40	45.31
Canola meal	9.31	9.29	9.27
Soybean meal	4.70	4.69	4.68
Cane molasses	6.13	6.12	6.10
Corn straw	27.92	27.86	27.80
Minerals	3.07	3.06	3.06
Calcium	1.03	1.03	1.03
Sodium bicarbonate	0.81	0.81	0.81
Yellow grease	1.53	1.53	1.52
DL-malic acid^a	–	0.21	0.42
Chemical composition^b;
Net energy, Mcal/kg
ENm	1.81	1.80	1.80
ENL	1.71	1.71	1.71
Crude protein (%)	11.46	11.44	11.42
NDF (%)	27.04	26.98	26.93
ADF (%)	15.98	15.95	15.92
NSC (%)	56.35	56.23	56.12
EE (%)	4.33	4.42	4.32

^a Sigma-Aldrich, St. Louis, MO, USA.

^b Based on tabular values for individual feed ingredients (NRC 2007) with the exception of supplemental yellow grease, which was assigned NE_m and NE_g values of 6.03 and 4.79, respectively (Zinn 1988).

To determine the milk composition, an aliquot obtained after milking was placed immediately in sterile plastics bags manufactured for liquid samples (Whirl-Pak®; Nasco, Fort Atkinson, WI, USA) and transported to the laboratory in portable coolers for determining composition analysis. Total solids were obtained by drying 2 mL of milk at 55°C for 48 h in air-forced oven. Dry samples were incinerated in a muffle furnace at 550°C for 3 h to calculate organic matter. Fat milk was obtained by Gerber method utilising 11.5 mL of milk for each 10.45 and 1 mL of sulfuric acid and iso-amilic alchohol, respectively. Milk protein concentration was obtained by phenolphthalein method (AOAC 2000). Production of milk components (total solids, fat and protein) was calculated by multiplying milk yield by component proportion on an individual ewe basis.

2.2. Statistical analyses

Data of milk composition and milk production and average daily gain of pre-weaned kids, which were recorded at weekly intervals of experiment, were analysed with a linear mixed model for repeated measures in a completely randomised design according to SAS (SAS Institute Inc. 2004, Cary, NC; Version 9.1), with evaluation of the covariance structures: Unstructured (UN), Compound symmetry (CS), and autorregresive AR(1), and the animal as random components. Feed additive effects (MA) were tested by means of orthogonal contrasts. Contrasts were considered significant when the P value was ≤0.05 and the tendencies were identified when the P value was >0.05 and ≤0.10.

3. Results and discussion

Based on the observed dry matter intake (DMI; Table 2) and the relative proportion of MA in diets (Table 1), daily intake of MA was equivalent to 0.0, 3.94 and 7.92 g/d/ewe for MAL₀, MAL₂ and MAL₄, respectively. Those doses of MA represent an average of 0.08 and 0.16 g MA/kg of live weight (LW) which is very similar than those used previously in dairy cattle (0.075 and 0.15 g MA/kg LW; Sniffen et al. 2006) and in dairy goats (0.14 mg MA/kg LW; Salama et al. 2002). Treatment effects on DMI, milk yield and milk composition are shown in Table 2. DMI was not affected (P ≥ 0.95) by MA supplementation. Lack of effects of MA supplementation on DMI have been a common response in lambs (Gonzalez-Momita et al. 2009; Aksu Elmali et al. 2012), dairy goats (Salama et al. 2002) and in lactating dairy cows (Sniffen et al. 2006; Khampa 2009). Because of the buffer activity of malate, it can be expected that there may be differences in DMI between the control groups and the supplemented goats when there is risk of acidosis. Even when ruminal pH was not measured in the present trial based on the diet formulation (NRC 2000, Level 1), the predicted ruminal pH for basal diet is 6.20; additionally, all diets were supplemented with 0.81% of sodium bicarbonate (Table 1). Thus, the absence of effects on DMI in the present experiment could be explained because the goats did not suffer digestive disorders.

Table 2. Effect of DL-MA supplementation on DMI, milk yield and milk composition of Pelibuey ewes.

	Treatments^a
Item	MA0	MA2	MA4	SEM	Linear	Quadratic
DMI (g/wk)	13.120	13.137	13.207	999	0.95	0.98
Milk yield (mL/wk)	9.764	11.269	12.970	1.040	0.04	0.94
Milk efficiency^b	0.74	0.86	0.98	0.07	0.03	0.82
Milk composition (%)
Protein	5.7	5.5	5.25	0.24	0.24	0.79
Fat	5.2	6.5	5.02	0.58	0.82	0.08
Total solids	15.0	16.3	15.78	0.76	0.46	0.36
Organic matter	94.8	94.8	94.69	0.32	0.75	0.93
Milk energy value (kcal/g)^c	286	295	281	20.46	0.46	0.36
Milk components yield (g/wk)
Protein	557	620	681	49	0.02	0.62
Fat	508	732	651	70	0.14	0.11
Milk energy (Mcal/wk)	2.792	3.324	3.645	213	0.01	0.48
FCM^d	9.053	11.785	11.813	1.47	0.14	0.12
Milk efficiency (adjusted to FCM)	0.69	0.89	0.89	0.12	0.25	0.11

^a MA₀ = no malic acid supplementation, MA₂ = 2 g of MA/kg of feed, and MA₄ = 4 g of MA/kg of feed.

^b Grams of milk production divided by grams of DMI.

^c Energy, Kcal/g = [203.8 + (8.36 × fat%) + (6.29 × CP%)], Baldi et al. (1992).

^d FCM = 6% fat-corrected milk calculated as follows: milk, g/wk × (0.453+ 0.0912F%), Mavrogenis and Papachristoforou (1988).

Milk yield (P = 0.04) and milk efficiency (P = 0.03) increased linearly as MA supplementation increased. The positive effects of milk production on dairy cows when diets have been supplemented with MA have been observed in previous studies (Khampa & Wanapat 2006; Sniffen et al. 2006). Similar to our results, Wang et al. (2009) reported that the milk yield increased (P = 0.04) by MA supplementation in dairy cows. The increases in milk production without changes in DMI promoted increases (linear, P = 0.03) in milk efficiency. The linear responses of milk production and milk efficiency as responses to the increases in MA supplementation levels observed in present experiment are in agreement with some studies carried out with dairy cows (Kung et al. 1982; Wang et al. 2009), although those researchers observed smaller increments compared to the present experiment. Salama et al. (2002) found that supplementation with MA was not beneficial for lactation performance with dairy goats, nevertheless, the supplemented goats gained more body weight than the control goats; therefore, supplemented goats showed more retained energy in tissue. Carboxylic acid salts activate the transformation of lactic acid into propionic acid through the S. rumnantium bacteria by using the succinate-propionate pathway (Martin et al. 2000), propionic acid is an essential substratum for glucose and lactose synthesis, and in this way malate increases the available energy for growth and for milk production (Martin & Streeter 1995). However, a few previous reports show that this does not have observed positive effects on milk production when malate was added to diets (Vicini et al. 2006; Foley et al. 2009). The reason for the difference among studies is unclear, but may be due to the differences in the basal content of MA in the diets or the dose of MA supplemented. For example, in the experiment of Foley et al. (2009), the diet had a high concentration of MA in the forages (high proportion of alfalfa) included in the basal diet. Even when we ignore the MA concentration in the basal diet, we can assume that the MA concentration in diet is low (<0.1%) because the source of forage used was maize straw which has a low content of MA (Callaway et al. 1997).

The inclusion of MA in diets had no effect on the percentage of total solids, organic matter, protein and fat content in milk (P > 0.05). This is in agreement with the previous reports that evaluated MA effects on milk composition of dairy cows (Kung et al. 1982; Sniffen et al. 2006; Foley et al. 2009) and in dairy goats (Salama et al. 2002). One could expect that the concentration of the milk components decreases as milk yield increases; this is because the correlation between concentrations of milk components is generally negative with milk production level (Torres-Hernandez & Hohenboken 1980). However, we found no effect of supplemental MA on milk contents percentage when milk production increased. Thus, total gross energy produced (Mcal/wk) was improved linearly (P = 0.01) as MA level increased. Greater milk yield constituents implies greater nutrient and energy availability for kids, which is important in the average daily gains and/or number of weaned animals, mainly when multiple births are presented in non-dairy breeds of sheep (Gavojdian et al. 2013). Likewise, Sniffen et al. (2006) suggested that protein yield increased (linear effect; P < 0.02) as MA doses increased. These researchers (Sniffen et al. 2006) attributed this effect to an increase in microbial efficiency as a result of the increases in carbohydrate use for microbial N production.

The ingestion of MA by the ewes resulted in a greater (linear, P < 0.01) average daily gain of their kids (Table 3). When milk is the sole source of food to pre-weaned kids, average daily gain and general condition of kids are a direct reflection of the amount and the quality of milk produced by the ewe (Cimen & Karaalp 2009). Therefore, the linear responses on ADG observed here is in agreement with greater milk and protein yield produced as the doses of MA were increased.

Table 3. Average daily gain of suckling Pelibuey lambs (data registered from the second to the fifth week of age) from ewes supplemented with 0, 2 or 4 g of malic acid/kg of feed^a.

	Treatment
Item	MA0	MA2	MA4	SEM	Linear	Quadratic
Average daily gain (g/d)
1–14 days	188	200	219	18.8	0.24	0.87
14–28 days	155	189	246	18.0	<0.01	0.62
1–28 days	170	195	232	14.1	<0.01	0.74

MA₀ = no malic acid supplementation, MA₂ = 2 g of MA/kg of feed, and MA₄ = 4 g of MA/kg of feed.

^a Weights of lambs registered during last four weeks of the first five weeks of birth.

4. Conclusion

It is concluded that, in Pelibuey ewes, the supplementation with 4 g of DL-MA per kilogram of feed increases milk production, milk protein yield and milk efficiency with no effect on DMI and milk composition. As a result of the characteristics of the diets used in the present experiment, this effect can be explained more by increases in energy efficiency promoted by malate intake, than its protective effect against acidosis. The increases in milk production led to a greater daily gain of suckling lambs fed with milk as the unique feed source in the first weeks of lactation. An additional consideration is that MA is an expensive feed ingredient that could add significantly to the feed cost even at low inclusion rates, thus, the use of MA as feed additive for lactating ewes depends on the relative price of additive and it's benefits on productivity.

Acknowledgement

The authors are grateful to Mr Liberato Montenegro (owner), Mr Saul Altamirano (manager) and DVM Hector Javier Morales Rodríguez (Veterinarian) from “Los Limones Ranch”.

Funding

This project was supported by CONACYT (Consejo Nacional de Ciencia y Tecnología) Project [No.147693].

Additional information

Funding

Funding: This project was supported by CONACYT (Consejo Nacional de Ciencia y Tecnología) Project [No.147693].